- move declaration of emptyLabelList (now deprecated) out of List.H

- can now safely use labelList::null() instead of emptyLabelList for
  return values. No special treatment required for lists.

  Possible replacements:

      if (notNull(list) && list.size())  ->  if (list.size())
      if (isNull(list) || list.empty())  ->  if (list.empty())

  The receiver may still wish to handle differently to distinguish
  between a null list and an empty list, but no additional special
  protection is required when obtaining sizes, traversing, outputting
  etc.

- relocate zone IO from Detail::MeshedSurfaceIOAllocator into surfMesh
  directly to allow re-purposing of MeshedSurfaceIOAllocator

- provide meshedSurf::emptySurface zero-sized placeholder implementation

- add concrete implementation of meshedSurf::zoneIds() to simplify
  overloading

- previously had a single pointer/value zeros (8 bytes), this meant
  that the reinterpret cast to a List would yield a reference that
  could be unsafe under certain conditions.

  Eg,
     const labelList& myList = labelList::null();

     Info<< myList.size() << nl; // OK since size is the first parameter

     SubList<label>(myList, 0);  // Unsafe

  The SubList usage is unsafe since it passes in pointer and size into
  the underlying UList. However, the pointer from the labelList::null()
  will be whatever happens to be around in memory immediately after the
  NullObject singleton. This is mostly not a problem if the List size
  is always checked, but does mean that the data pointer is rather
  dubious.

- Increase the size of the nullObject singleton to 32 bytes of zeros
  to ensure that most reinterpret casting will not result in objects
  that reference arbitrary memory.

  The 32-byte data size is rather arbitrary, but covers most basic
  containers.

Feature object registry search

See merge request OpenFOAM-plus!232

  - objectRegistry search, erase methods
  - clip, minMax
  - function object triggering
  ...

- The findObject() methods are template-typed and used to locate a
  particular Type/name combination.

  Eg,

      volScalarField* ptr = obr.findObject<volScalarField>("xyz");

- The findIOobject() methods are un-typed and use the name only.

  Eg,

      regIOobject* ptr = obr.findIOobject("xyz");

The typed versions will be most commonly used, but the un-typed lookup
can be useful in a templating.

- Simplified findObject* methods to use findIOobject* as the backend.

- similar to what erase() does, but as a mutable operation (#1180)

- replace basicThermo lookupAndCheckout (commit 880c9875) with
  the new objectRegistry::checkOut() method.

- implemented as lazy evaluation with an additional update() method.
  This avoids unnecessary changes until the values are actually
  required.

- apply mesh motion changes for momentum, volFieldValue,
  specieReactionRates function objects

- forwards to the underlying HashTable erase, but frees things owned
  by the registry as well (ie, performs a checkOut)

- also removed some editing cruft from controlDict that should not
  have been there

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56480

from e to T. T proved to be more generic solution.

Add minMax and clip field functions

See merge request OpenFOAM-plus!230

STYLE: avoid local variable name masking