Allow garrisoned entities to transform into one that cannot garrison.

[Freagarach]

Currently, when an entity that is garrisoned transforms (upgrades/promotes) into an entity that cannot garrison the formerly garrisoned holder, several things go wrong.

• The garrison flag is not updated (should be done in eject, not perform eject. (Simple) (​Phab:D3628)
• The entity that was transformed disappears. This is because first the position of the transforming entity is used to set on the newly created entity -- Garrisoned, thus out of world. Only thereafter a message is sent to the GarrisonHolder to ungarrison (the transforming entity gets ejected and thus receives a position InWorld) and to garrison the new entity if possible (which it is not). Hence the new entity has a position out of world and can thus neither be selected nor seen by the player. (​Phab:D3650)

[Freagarach]

In 24977:

Let entities garrison using cmpGarrisonable.

Followup to r24957 / rP24957.
Moves the logic for garrisoning from cmpGarrisonHolder to the entity that is being garrisoned.
Also fixes ​https://wildfiregames.com/forum/topic/36863-teleportation-feature-in-a24/?do=findComment&comment=418441 while at it (setting garrisoned before transferring orders on transform).

Differential revision: D3280
Refs: #5906
Comments by: @Stan, @wraitii

[Freagarach]

In 25019:

Ungarrison entities using cmpGarrisonable.

Follow-up to r24977 / rP24977.
This moves responsibilities even further to the garrisoning entity.

Fixes the garrison flag when renaming entities cannot garrison (#5906).
Allows easy fixing of #6087.

Ticket: #6081
Differential revision: D3628
Comments by: @Stan, @wraitii (also in length on IRC)