Layers and layer groups did not generate message bus callbacks.
This was a regression from 4.2. The fix adds
`WM_msg_publish_rna_prop` to (some) places where the layers/groups
change or the active one changes.
Also resolves#129539.
Note: This does not cover every possible scenario and only fixes
the regressions from 4.2. The message bus is still very unreliable
when it comes to detecting changes of properties.
Pull Request: https://projects.blender.org/blender/blender/pulls/130039
589ef9ccce