Improves airlock closing and density/crush()

So you can slip through/shoot projectiles through doors that are closing if their animation hasn't completed.

Airlocks will automatically reopen if the safeties are on and mob/living is between them, similar to an elevator door. If the safeties are not on, it'll crush whatever's in between the doors. This can be seen as either a nerf or a buff to door crushing, since it's not immediate stun before the animation has finished but also means people don't get blocked by a closing door who's animation hasn't finished.

This applies to blast doors/shutters as well, but blast doors don't have safeties so they'll crush you regardless like they always have.

Fixes https://github.com/tgstation/-tg-station/issues/5935