Fix an issue where the versioning of Action & slot assignments did not
use RNA properties to do the slot assignment. This caused certain
on-update callbacks to be missed, which in turn meant that an Action
constraint could remain disabled even though its action slot assignment
had been corrected.
This is now resolved by actually using RNA to set the assigned slot in
the versioning code.
Unfortunately that does mean that any reporting done will be by the
generic RNA code as well, and won't be specific to versioning. This
shouldn't be much of an issue in practice, as any warning was only shown
in the rare case of mis-matched `action.idroot` properties.
Pull Request: https://projects.blender.org/blender/blender/pulls/134759
3dbede128e