Z-Mimic (#3907)

* Openturf icon fixes and improvements

* more things

* Remove some pointless/bad layering/planing

* yeah well I didn't need this anyways

* Refactor Z mimickry to be at /turf

* more refactoring

* Cleanup, use turf/flags instead of z_mimic_flags

* Fix turf/Entered()

* misc optimizations

* fixes

* Major icon smoothing optimizations

* Speed up boot some more

* Fix AO

* Remove some redundant code

* Tie Z-lights to Z-mimic instead of openturfs

* Fix an opacity issue with no_mutate turfs

* Fix some issues with Z-mimic AO not properly clearing

* Fix some OT->OT changetuf bugs

* Add helpers for changing Z-mimic operational state on turfs

* Fix some merge issues, change how F_CUT smoothhint works a bit.

* indentation

* SSopenturf -> SSzcopy

code/modules/lighting/lighting_source.dm

@@ -402,8 +402,8 @@
 				T = T.above
 				goto check_t
 		else
-			if (isopenturf(T) && T:below)	// Not searching upwards and we have a below turf.
-				T = T:below	// Consider the turf below us as well. (Z-lights)
+			if (T && (T.flags & MIMIC_BELOW) && T.below)	// Not searching upwards and we have a below turf.
+				T = T.below	// Consider the turf below us as well. (Z-lights)
 				goto check_t
 			else // Not searching upwards and we don't have a below turf.
 				zlights_going_up = TRUE