Previous commit solved: "mixture rho to volume-based in rhoThermo."
This proved to work correctly for rho=constant EoS but not for
idealGas. Fixes #2304. The previous gitlab issue was #1812.

- `functions<scalar>` and `functions<vector>` were erroneously
   documented in header as `lookup<scalar>` etc.

INT: handle fluent square brackets (fixes #2429)

- patch applied from openfoam.org

- support direct processing of CompactListList instead of requiring
  a conversion to labelListList for bandCompression and renumbering
  methods.

- manage FIFO with CircularBuffer instead of SLList (avoids
  allocations in inner loops). Invert logic to use a bitSet of
  unvisited cells, which improves looping as the matrix becomes more
  sparse.

- fix missed weighting in bandCompression (same as #1376).
  In polyTopoChange, handle removed cells immediately to simplify
  the logic and align more closely with bandCompression.

STYLE: enclose bandCompression within meshTools namespace

ENH: PrimitivePatch pointFaces with DynamicList instead of SLList

- MPI_Gatherv requires contiguous data, but a byte-wise transfer can
  quickly exceed the 'int' limits used for MPI sizes/offsets. Thus
  gather label/scalar components when possible to increase the
  effective size limit.

  For non-contiguous types (or large contiguous data) now also
  reverts to manual handling

ENH: handle contiguous data in GAMGAgglomeration gather values

- delegate to globalIndex::gatherValues static method (new)

- supports gatherv of label and scalar types

- combine blocking and non-blocking interfaces in UPstreamWrapping
  (code reduction).

DEFEATURE: remove unused UPstream allToAllv wrapping

- backend interface preserved in UPstreamWrapping

COMP: add genericListBroadcast - simplifies code

- bundles frequently used 'gather/scatter' patterns more consistently.

  - combineAllGather     -> combineGather + broadcast
  - listCombineAllGather -> listCombineGather + broadcast
  - mapCombineAllGather  -> mapCombineGather + broadcast
  - allGatherList        -> gatherList + scatterList
  - reduce               -> gather + broadcast (ie, allreduce)

- The allGatherList currently wraps gatherList/scatterList, but may be
  replaced with a different algorithm in the future.

STYLE: PstreamCombineReduceOps.H is mostly unneeded now

STYLE: LduInterfaceFieldPtrsList as alias instead of a class

STYLE: define patch lists typedefs when defining the base patch

- eg, polyPatchList typedef within polyPatch.H

INT: relocate GeometricField::Boundary -> GeometricBoundaryField

- was internal to GeometricField but moving it outside simplifies
  forward declarations etc. Code adapted from openfoam.org

Two problems:
- flipping inside snappyHexMesh is not done in a parallel
consistent way. So e.g. the octree-cached inside/outside information
has already been calculated. For now flipping of
distributedTriSurfaceMesh is disabled.
- octree-cached inside/outside information was using already
cached information and would only work for outwards pointing
volumes

- 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.