Blender Git Loki

Fix T84600: prevent bone groups operators on proxies and library
overrides

Editing bone groups is not supported on proxies/overrides [changes a re
lost on file reload], need to do proper polling (and also prevent this
from rna) for:

- adding bone groups
- removing bone groups
- renaming bone groups
- setting bone groups colors

Previously, this was hinted at by setting the layout inactive, with
preoper polls, this is now not needed anymore.

note: Selection of bone groups actually makes sense here and is
supported, so this is not prevented in this patch, but UI wise this is
not nice in the override case, because one cannot set an active_index
(aka select) in the UI list.

Maniphest Tasks: T84600

Differential Revision: https://developer.blender.org/D10131