Put VTK symbols inside ABI namespace macros.

VTK_ABI_NAMESPACE_{BEGIN,END} macro is inserted around all VTK symbols.

Exclusions:
 * C interfaces, such as GetVTKVersion and the python module.
 * third-party libraries and external libraries that are not maintained
   by VTK but are part of the VTK repository.
 * Cxx module tests
 * Utilities
 * Wrapping/Tools