PSprites (Overlays) support for Non-Players

[Major Cooke]

I'm certain most people here remember overlays being a submission for non-actors by Leonard2, only it's been lost to time since ZScript had started and made the pull request completely incompatible.

What ZScript currently cannot do is render psprites when inside the head of a non-player actor.

Right now, the only way one can have something even remotely close to psprites is by using statusbar/ACS hudmessage hacks. Not good.

[Graf Zahl]

I'M putting this on hold for the time being. While interesting it's a very time consuming feature to add because the entire overlay system has to be transitioned away from player_t.