Blender Git Loki

Fix T53909: Joining armatures did not remap names on merged action data

Technically this was not a bug, as this functionality was not meant to
work. (Drivers were already handled though, as they are part of the rig)
It was assumed that there was little value in having this functionality
available, as in most pipelines, animation production only begins after
the rig has been locked down (see bug report comments for more details).

On reflection, in most common situations, there's probably no harm in
doing these rna path fixups. This commit takes advantage of some similar
code I recently put in place in the Grease Pencil branch (for joining GP
objects and their layers).

Important Note for Animators/Riggers/TD's:
Please be aware that after joining armatures, some of the animation may
still need to be redone (due to changes in the transform hierarchies/
transform spaces that the animation is applied in). We do not attempt
to correct for these problems, and it is unlikely that we will in future.