When inserting keys, look on related IDs for an action to reuse that.
This will make use of the slot system on the new layered action to ensure
the animation data doesn't collide.
This is done on the `id_action_ensure` function since that is the common
function to get an action off an `ID`.
IDs with more than 1 user will be skipped.
"Related ID" in this case is hardcoded with a `switch` statement for each ID type.
The system builds a list starting from the ID that should be keyed and
keeps expanding the list until an action is found or no more
non-duplicate IDs can be added. (This is using linear search for duplicate checks,
but I don't think we will deal with a lot of IDs in this case)
Pull Request: https://projects.blender.org/blender/blender/pulls/126655
cb6ed12ef1