Add a DISABLE_DREAMLUAU define, for disabling dreamluau at compile-time (#89359)

## About The Pull Request

this adds a new define, `DISABLE_DREAMLUAU` (commented out by default),
which does... exactly what it says on the tin. it fully disables any
dreamluau-related code (the "Open Lua Editor" admin verb is left in,
albeit just giving the user a warning saying Lua is disabled, just so
there's no confusion about the verb itself being missing)

when compiling with OpenDream outside of CI (so dreamluau code will
still be linted), `DISABLE_DREAMLUAU` will be defined by default, tho.

## Why It's Good For The Game

makes OpenDream testing easier

## Changelog

no user-facing changes. or even code changes for most cases.

code/modules/admin/verbs/lua/lua_editor.dm

@@ -1,3 +1,4 @@
+#ifndef DISABLE_DREAMLUAU
 /datum/lua_editor
 	var/datum/lua_state/current_state
 
@@ -279,7 +280,12 @@
 /datum/lua_editor/ui_close(mob/user)
 	. = ..()
 	qdel(src)
+#endif
 
 ADMIN_VERB(lua_editor, R_DEBUG, "Open Lua Editor", "Its codin' time.", ADMIN_CATEGORY_DEBUG)
+#ifndef DISABLE_DREAMLUAU
 	var/datum/lua_editor/editor = new
 	editor.ui_interact(user.mob)
+#else
+	to_chat(user, span_warning("Lua support has been disabled at compile-time."), type = MESSAGE_TYPE_ADMINLOG, confidential = TRUE) // doing this instead of just disabling the verb entirely so it's clear WHY it doesn't work.
+#endif