Port SSoverlays & Convert turfs to use it (#5004)

* Added "Display Initialize() Log" admin debug command so you can see it mid-round.

* Ported the core of the overlays management subsystem from /tg

- Added SSoverlays subsystem for compiling overlay lists and applying them to atoms in a controlled anti-lag subsystem.
- Added vars and procs to atom which should eventually replace all direct interaction with BYOND's /atom/overlays var outside the subsystem.
- Added OVERLAY_QUEUED flag to var/atom/flags bitfield.
- Added small framework for subsystem performance tracking. So far used only by SSoverlays
- Added admin debug command "Display overlay Log" to see performance stats mid-round.

* Fix runtime on universal pipe adaptor update_icons

* Workaround for appearance_bro not initialized

Unfortuantely BYOND's initialization order is strange, and the appearance_bro var is only half initialized when map starts to load, causing errors.  We temporarily fix by moving it to be a global-scoped global.

* Convert fire alarms to use add_overlay() A good first test.

* Convert turfs to use add_overlays(), eliminating the turf_overlay_holder!

- Converted as much as I could find about turf overlays to use add_overlay().
- This should be enough to stop BYOND from crashing, so we can eliminate the turf_overlay_holder hack.
- This also lets us remove the anti-corruption hacks from walls and open space.
- ZAS gas overlays can use priority overlays, so this also fixes the gas-goes-away-when-crowbarring-plating issue.
- Stuff like that

* Convert turf overlay interactions to use add_overlay.

Note: This is a plain and simple conversion of existing code to use SSoverlays. However I look at the line changed, and note that that line likely never fully worked as intended, as it has no way of re-applying itself.
I would make it use a priority overlay, but there is no code present for *removing* said overlay from neighbors when it is no longer required.  That code should be implemented by original author.

code/modules/admin/verbs/debug.dm

@@ -327,6 +327,36 @@
 
 	usr << browse(dellog.Join(), "window=dellog")
 
+/client/proc/cmd_display_init_log()
+	set category = "Debug"
+	set name = "Display Initialize() Log"
+	set desc = "Displays a list of things that didn't handle Initialize() properly"
+
+	if(!check_rights(R_DEBUG))	return
+	src << browse(replacetext(SSatoms.InitLog(), "\n", "<br>"), "window=initlog")
+
+/client/proc/cmd_display_overlay_log()
+	set category = "Debug"
+	set name = "Display overlay Log"
+	set desc = "Display SSoverlays log of everything that's passed through it."
+
+	if(!check_rights(R_DEBUG))	return
+	render_stats(SSoverlays.stats, src)
+
+// Render stats list for round-end statistics.
+/proc/render_stats(list/stats, user, sort = /proc/cmp_generic_stat_item_time)
+	sortTim(stats, sort, TRUE)
+
+	var/list/lines = list()
+	for (var/entry in stats)
+		var/list/data = stats[entry]
+		lines += "[entry] => [num2text(data[STAT_ENTRY_TIME], 10)]ms ([data[STAT_ENTRY_COUNT]]) (avg:[num2text(data[STAT_ENTRY_TIME]/(data[STAT_ENTRY_COUNT] || 1), 99)])"
+
+	if (user)
+		user << browse("<ol><li>[lines.Join("</li><li>")]</li></ol>", "window=[url_encode("stats:\ref[stats]")]")
+	else
+		. = lines.Join("\n")
+
 /client/proc/cmd_admin_grantfullaccess(var/mob/M in mob_list)
 	set category = "Admin"
 	set name = "Grant Full Access"