Add guards to the RNA code to prevent the creation of legacy data on a
layered Action, and vice versa.
On a legacy Action, it is now impossible to create new layers or bindings.
On a layered Action, it's now impossible to create legacy F-Curves or
groups.
Refactor: Anim: rename bl_animation_id.py to bl_animation_action.py
The `Animation` datablock is no more, and this file tests `Action`.
No functional changes.
Pull Request: https://projects.blender.org/blender/blender/pulls/122483
