Merge topic 'htg-generate-fields'

fb1d186d Fix doxygen warning
704a63eb Add default constructors/destructors
61f54b61 Fix header test
9ece3eb7 Add export macros
437ec50f Add python support for vtkBitArray
941019df Use bit array instead of bool implicit
ba543719 Add test for field data total visible volume
27bddc5c Field data addition
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !11910