Can 64-bit option rely on VTK for consistency?

[jspanchu]

Is your feature request related to a problem? Please describe.
It is strange when we intermix code that uses vtk filters and ttk filters. Some assumptions on the 'id' data type can no longer be safe. (int vs long long, ttk::SimplexId vs vtkIdType)

Describe the solution you'd like
It would be nice if ttk::SimplexId and vtkIdType were consistent when TTK is built with ParaView/VTK support.
The cmake config script can check to see if VTK was built with support for 64-bit id type. If it were the case, then we turn on TTK_ENABLE_64_BIT_IDS. By default, this option is turned off config.cmake:98

[JonasLukasczyk]

This seems reasonable to me. +1

[julien-tierny]

in principle, that makes sense.
two things:

• we first need to carefully check that all our tests indeed work as expected when switching to 64 bits
• we need to assess the performance loss induced by the 64 bit comparisons (instead of 32 bit comparisons) and there WILL be some.

[jspanchu]

Fair enough. Let me know if there is anything I can do to help!