Fix #135923: Library Overrides break action constraints

Fix an issue with library overrides that was caused by Action
assignments getting versioned too late in the versioning process. Now
the versioning of Action assignments (which assigns the
created-by-versioning action slots) happens in the 'after linking'
stage, as well as in the 'after setup' stage. The latter is still
necessary for the conversion of pre-2.5x animation data.

It is likely that the versioning code can now be simplified, as the
tagging for "this needs upgrading" may no longer be necessary. We're now
too close to the 4.4 release to comfortably make such bigger refactors,
though, so I'd rather keep the overall code structure as-is.

Pull Request: https://projects.blender.org/blender/blender/pulls/135988

source/blender/blenloader/intern/versioning_400.cc

@@ -1520,6 +1520,7 @@ void do_versions_after_linking_400(FileData *fd, Main *bmain)
   if (!MAIN_VERSION_FILE_ATLEAST(bmain, 404, 2)) {
     blender::animrig::versioning::convert_legacy_animato_actions(*bmain);
     blender::animrig::versioning::tag_action_users_for_slotted_actions_conversion(*bmain);
+    blender::animrig::versioning::convert_legacy_action_assignments(*bmain, fd->reports->reports);
   }
 
   if (!MAIN_VERSION_FILE_ATLEAST(bmain, 404, 7)) {