Building on top of T286547: Translatable modules: Message group for MessageBundle, we should ensure that we hook into the relevant page actions (create, move, delete) and ensure the system state does not get corrupted.
- Page creation: already handled
- Page move: message bundle and messages need to be renamed (if difficult, start by blocking moves)
- Page deletion: delete message bundle (okay to leave translations behind as is common, but warning would be nice)