Trigger an exit-reentry when the target entity of an order is renamed

This lets unitAI FSM states correctly handle target entity renaming by processing a message when that happens. The default behaviour is to leave-reenter the state, which re-runs sanity checks and optionally picks a better behaviour.

UnitMotion is still not made aware of entity renaming, as the leave-enter makes it irrelevant in practice. It still may be a good idea to implement that someday.

Fixes the concern raised at rP20393.
Fixes #5584

Comments by: bb, Freagarach

Tested by: Freagarach

Reported by: minohaka, bb, Freagarach, gameboy (error in the original commit)

Differential Revision: https://code.wildfiregames.com/D2735