[MIRROR] Fixes critical plane masters improperly not being readded in show_to [MDB IGNORE] (#19060)

Fixes critical plane masters improperly not being readded in show_to (#72604)

## About The Pull Request

[Adds support for pulling z offset context from an atom's
plane](https://github.com/tgstation/tgstation/commit/9f215c5316e5cfdbedf6a23ff97dfee0e523354b)

This is needed to fix paper bins, since the object we plane set there
isn't actually on a z level.
Useful elsewhere too!

[Fixes compiler errors that came from asserting that plane spokesmen had
a plane
var](https://github.com/tgstation/tgstation/commit/b830002443f2fbe230e9ff00236d7a46a9f2eec7)

[Ensures lighting backdrops ALWAYS exist for each lighting
plane.](https://github.com/tgstation/tgstation/commit/0e931169f7c5336333bc6f41353c82f603fc1170)

They can't float becuase we can see more then one plane at once yaknow?

[Fixes parallax going to shit if a mob moved zs without having a
client](https://github.com/tgstation/tgstation/commit/244b2b25baecfc644505a3ea1e348e0cb97a04e0)

Issue lies with how is_outside_bounds just blocked any plane readding
It's possible for a client to not be connected during z moves, so we
need to account for them rejoining in show_to, instead of just blocking
any of our edge cases.

Fixing this involved having parallax override blocks for show_plane and
anything with the right critical flags ensuring mobs have JUST the right
PMs and relays.
It's duped logic but I'm unsure of how else to handle it and frankly
this stuff is just kinda depressing.
Might refactor later

[show_to can be called twice successfully with no hide_from
call.](https://github.com/tgstation/tgstation/commit/092581a5c06f7f884f48d41c96fa9300327ef214)

Ensures no runtimes off the registers from this

## Why It's Good For The Game

Fixes #72543
Fixes lighting looking batshit on multiz. None reported this I cry into
the night.

## Changelog
🆑
fix: Fixes parallax showing up ABOVE the game if you moved z levels
while disconnected
/🆑

---------

Co-authored-by: LemonInTheDark <58055496+LemonInTheDark@users.noreply.github.com>
Co-authored-by: Time-Green <timkoster1@hotmail.com>

code/datums/components/seethrough.dm

@@ -102,13 +102,14 @@
 	for(var/atom/movable/screen/plane_master/seethrough in our_hud.get_true_plane_masters(SEETHROUGH_PLANE))
 		seethrough.unhide_plane(fool)
 
-	var/image/user_overlay = new(parent)
-	user_overlay.loc = parent
+	var/atom/atom_parent = parent
+	var/image/user_overlay = new(atom_parent)
+	user_overlay.loc = atom_parent
 	user_overlay.override = TRUE
 
 	if(clickthrough)
 		//Special plane so we can click through the overlay
-		SET_PLANE_EXPLICIT(user_overlay, SEETHROUGH_PLANE, parent)
+		SET_PLANE_EXPLICIT(user_overlay, SEETHROUGH_PLANE, atom_parent)
 
 	//These are inherited, but we already use the atom's loc so we end up at double the pixel offset
 	user_overlay.pixel_x = 0