The motivation for these changes was to properly support extracting of
non-leaf blocks from a composite dataset (ref: paraview/paraview#18696).
This, however, resulted in changes to cleanup the vtkSelector along the
following lines:

Cleanup virtual API to avoid passing parameters that most subclasses
ended up ignoring. `ComputeSelectedElements` was provided composite
and amr indices which was not necessary. Fixed that.

Better handle composite datasets where selection was defined using
non-leaf nodes. Previous API was not able to support this use-case.