Visible Garrisoning in animated gate bug

[Stan]

It would be nice to to have animated meshes like boats with units on them, without losing the animation.

This currently works with siege towers however it doesn't work well with things like gates.

To reproduce this download the terra magna mod and play around garrisoning the Chinese gate. If it's not locked and you garrison units inside it the gate will stay open. If it's locked, it'll stay closed, and correctly switch to the right anim when opening then it won't close anymore.

Another story happens with garrison flags. If the gate is garrisoned the flags will appear. They'll have their Idle animation set. What will happen is if you try to move units near the gate the same bugs as before will occur and also the flags will freeze as they will be set to an anim they do not have, such as gate_opening, gate_closing, gate_closed, gate_opened. They ought to play Idle in this case.

[sanderd17]

In 18266:

Allow simulation to set the actor variant selection, and use it for the garrison flag. Fixes #3952 Refs #2679, #3983