This adds the following options to Select Grouped in pose mode:
* Children
* Immediate Children
* Parents
* Siblings
Doing so means we are more in line with similar operators in edit mode.
Unfortunately re-using existing functionality from edit mode doesn't seem
possible due to the edit/pose bone difference.
The added functionality can handle multiple armatures in pose mode at once.
Also the same operators can be accessed from weight paint mode.
Implements #137274
Pull Request: https://projects.blender.org/blender/blender/pulls/137960
717fa42e5e