Add per-block pickability to some OpenGL2 mappers.
- Add pickability to
vtkCompositeDataDisplayAttributes
per-block state. - Have
vtkGlyph3DMapper
accept avtkCompositeDataDisplayAttributes
instance named BlockAttributes; use it to specify visibility and pickability when the input (not source) data is composite. - Have
vtkCompositePolyDataMapper2
heed per-block pickability. - Test both mappers using hardware selection.