Fix keyframe properties not being editable when animating a
library-overridden datablock.
The problem was that RNA pointers were created based on the datablock
affected by the animation (for example an Object), instead of the
datablock that contains the FCurve itself (the Action). The latter can
be local to the current blend file and should thus be editable, even
when the former is not.
Reviewed By: mont29
Maniphest Tasks: T81965
Differential Revision: https://developer.blender.org/D10091
c3b68fa7b1