expose block selection for multiblock volume rendering
requested to merge utkarsh.ayachit/paraview:19123-volume-rendering-of-multblock-datasets into master
We had lost ability to choose the block to volume render when dealing with multiblock datasetes. Bringing that back. Fixes #19123 (closed).
pqCompositeTreePropertyWidget/pqCompositeDataInformationTreeModel was updated to not allow user to select non-leaf nodes for volume rendering since volume rendering only supports leaf nodes.
Closes #19123 (closed)