INT: coherent: enable serial write of volFields

- Tested by writing volFields with the icoFoam's cavity test case
  (boundary file is still needed in polyMesh)

- ASCII field files have some formatting issues (writing is done with
  dictionary::write)

- OFCstream now inherits from OCharStream; rename foam-extend flavored
  member functions to OF equivalents

- New regIOobject virtual member function "writeToStream" allows to
  construct OFCstream within GeometricField

- The heavy data is given to the OFCstream in the Field class.
  Doing this makes it simple to ensure that every rank will call
  OFCstream::write for every field.

Co-authored-by: Mark Olesen <>