- percent of cells is taken relative to selection size.
- percent of faces is taken relative to the number of boundary faces
  that do not fix velocity themselves.

ENH: avoid correctBoundaryConditions() if values were not limited

- areaWrite and fileFieldSelection

- when writing surface formats (eg, vtk, ensight etc) the sampled
  surfaces merge the faces/points originating from different
  processors into a single surface (ie, patch gatherAndMerge).

  Previous versions of mergePoints simply merged all points possible,
  which proves to be rather slow for larger meshes. This has now been
  modified to only consider boundary points, which reduces the number
  of points to consider. As part of this change, the reference point
  is now always equivalent to the min of the bounding box, which
  reduces the number of search loops. The merged points retain their
  original order.

- inplaceMergePoints version to simplify use and improve code
  robustness and efficiency.

ENH: make PrimitivePatch::boundaryPoints() less costly

- if edge addressing does not already exist, it will now simply walk
  the local face edges directly to define the boundary points.

  This avoids a rather large overhead of the full faceFaces,
  edgeFaces, faceEdges addressing.

  This operation is now more important since it is used in the revised
  patch gatherAndMerge.

ENH: topological merge for mesh-based surfaces in surfaceFieldValue

- similar to edge valid(), true if vertices are unique, non-negative

- Pstream changes, coordSetWriters etc.

- similar to how noOp was defined, but with perfect forwarding

STYLE: combine Swap into stdFoam

STYLE: capitalize FileOp, NegateOp template parameters

- lower memory overhead, simpler code and eliminates need for
  ListListOps::combineOffset()

- optional handling of local faces/points for re-using in different
  contexts

STYLE: labelUList instead of labelList for globalMesh mergePoints

STYLE: adjust verbose information from mergePoints

- also report the current new-point location

- also disables PointData if manifold cells are detected.
  This is a partial workaround for volPointInterpolation problems
  with handling manifold cells.

- additional verbosity option for conversions

- ignore old `-finite-area` option and always convert available
  finiteArea mesh/fields unless `-no-finite-area` is specified (#2374)

ENH: simplify point offset handling for ensight output

- extend writing to include compact face/cell lists

- a try/catch approach is not really robust enough (or even possible)
  since read failures likely do not occur on all ranks simultaneously.
  This leads to situations where the master has thrown an exception
  (and thus exiting the current routine) while other ranks are still
  waiting to receive data and the program blocks completely.

  Since this primarily affects data conversion routines such as
  foamToEnsight etc, treat similarly to lagrangian: check for the
  existence of essential files before proceeding or not. This is
  wrapped into a TryNew factory method:

      autoPtr<faMesh> faMeshPtr(faMesh::TryNew(mesh));
      if (faMeshPtr) ...

- these are the same thing now and 'broadcast' expresses the intention
  more directly/consistently

- gather/scatter types of operations can avoid AllToAll communication
  and use simple MPI gather (or scatter) to establish the receive sizes.

  New methods: finishedGathers() / finishedScatters()

BUG: masterUncollatedFileOperation checking of file-size

- used Foam:fileSize check to decide on scheduled/nonBlocking but this
  was being done on all ranks and subsequently broadcast.
  Now avoid unnecessary filesystem access on non-master ranks.

- both schemes and solutions data are treated as MUST_READ_IF_MODIFIED
  even if the requested readOption is nominally MUST_READ or
  READ_IF_PRESENT, but now delay this change.

- in preparation for broadcasting versions

- allows simpler handling of processor conditions etc.

ENH: modernize constructor for better alignment with polyPatch

STYLE: pass value not reference to pTraits for basic types

STYLE: add solveVector typedef to vector.H

- do not need contruct or move assign from SortableList.
  Rarely (never) used and can simply treat like a normal list
  by applying shrink beforehand.

- make append() methods return void instead of returning self, which
  makes it easier to derive from. Having them return self was a bit of
  an original design mistake.
  Chaining appends do not actually occur anywhere. Even if they were
  to be used, would not want to rely on them (fear of slicing on any
  derived classes).

BUG: IndirectList iterator comparison loses constness

- simple wrapper for (!headerClassName().empty()) when checking if
  reading was successful.

- eliminate redundant size_ accounting

- drop extra 'Container' template parameter and replace functionality
  with more flexible pack/unpack methods.
  There is also a pack() method that handles indirect lists of lists
  that can be used, for example, to pack a patch slice of faces.

  Drop the 'operator()' method in favour of unpack to expose and properly
  document the conversion. Should revisit the corresponding code in
  some places for optimization potential.

- align some method names with globalIndex:
  totalSize(), maxSize() etc

- less communication than gatherList/scatterList

ENH: refine send granularity in Pstream::exchange

STYLE: ensure PstreamBuffers and defaultCommsType agree

- simpler loops for lduSchedule

- can restrict calculation of D32 and other spray properties to a
  subset of parcels. Uses a predicate selection mechanism similar to
  vtkCloud etc.

ENH: code cleanup in scalar predicates

- pass by value not reference in predicates
- additional assign() method to refactor common code

refactor coordSet writers (#2347)

See merge request !524

- with the special setFormat "probes", all of the sampled sets are
  treated more similarly to probes, with an ensemble output to raw
  probed format.

  This is of course less useful when the number of sampled points
  becomes very large.

- can now specify sampled sets as dictionary entries instead of a list
  entry.
    can now use:  sets { ... }
    instead of:   sets ( ... );

  This is similar to sampled surfaces and makes it easier to
  manage with dictionary manipulation tools.

TUT: update to use writeTime instead of outputTime

- in v2112 the functionObject results were only delivering values from
  the last set listed (ie, overwritten).

  Now that the values are properly scoped by the name of the set itself
  Eg, `average(lines,p)` for the average for 'lines' set, existing
  workflows will break.

  It thus makes reasonble sense to also handle results without a
  qualifier as ensemble values.

      average(p)    // Ensemble average of all listed sets

- the very old 'writer' class was fully stateless and always templated
  on an particular output type.

  This is now replaced with a 'coordSetWriter' with similar concepts
  as previously introduced for surface writers (#1206).

  - writers change from being a generic state-less set of routines to
    more properly conforming to the normal notion of a writer.

  - Parallel data is done *outside* of the writers, since they are used
    in a wide variety of contexts and the caller is currently still in
    a better position for deciding how to combine parallel data.

ENH: update sampleSets to sample on per-field basis (#2347)

- sample/write a field in a single step.

- support for 'sampleOnExecute' to obtain values at execution
  intervals without writing.

- support 'sets' input as a dictionary entry (as well as a list),
  which is similar to the changes for sampled-surface and permits use
  of changeDictionary to modify content.

- globalIndex for gather to reduce parallel communication, less code

- qualify the sampleSet results (properties) with the name of the set.
  The sample results were previously without a qualifier, which meant
  that only the last property value was actually saved (previous ones
  overwritten).

  For example,
  ```
    sample1
    {
        scalar
        {
            average(line,T) 349.96521;
            min(line,T)     349.9544281;
            max(line,T)     350;
            average(cells,T) 349.9854619;
            min(cells,T)    349.6589286;
            max(cells,T)    350.4967271;
            average(line,epsilon) 0.04947733869;
            min(line,epsilon) 0.04449639927;
            max(line,epsilon) 0.06452856475;
        }
        label
        {
            size(line,T)    79;
            size(cells,T)   1720;
            size(line,epsilon) 79;
        }
    }
  ```

ENH: update particleTracks application

- use globalIndex to manage original parcel addressing and
  for gathering. Simplify code by introducing a helper class,
  storing intermediate fields in hash tables instead of
  separate lists.

ADDITIONAL NOTES:

- the regionSizeDistribution largely retains separate writers since
  the utility of placing sum/dev/count for all fields into a single file
  is questionable.

- the streamline writing remains a "soft" upgrade, which means that
  scalar and vector fields are still collected a priori and not
  on-the-fly.  This is due to how the streamline infrastructure is
  currently handled (should be upgraded in the future).

Automatic hole closure:
- introduces 'holeToFace' topoSet source
- used when detecting a 'leak-path'
- creates additional baffles to close the leak

Multi-stage layer addition:
- Can add layers in multiple passes

See issues: #2403, #2404