Reworks on-mob overlay icon generation. (#8920)

* Porting species equip_adjust from Neb.

* get_species() => get_species_name(), adds correct get_species() impl

* sprite_sheets is now crudely lazylisted.

* Adds returns to add_blood and add_accessories.

* apply_addblends now uses an overlay.

* Renames the various worn overlay procs to be more informative.

* Debugging/refining overlay gen.

* Adding handling for string icon paths.

* Refining/debugging offset overlay gen.

* Getting the offset system working.

* Commenting out Teshari offsets for the time being.

code/_helpers/icons.dm

@@ -1033,3 +1033,21 @@ GLOBAL_LIST_EMPTY(cached_examine_icons)
 
 	//Animate it growing
 	animate(img, alpha = 0, transform = matrix()*grow_to, time = anim_duration, loop = loops)
+
+// For checking if we have a specific state, for inventory icons and nonhumanoid species.
+// Cached cause asking icons is expensive. This is still expensive, so avoid using it if
+// you can reasonably expect the icon_state to exist beforehand, or if you can cache the
+// value somewhere.
+var/global/list/_icon_state_cache = list()
+/proc/check_state_in_icon(var/checkstate, var/checkicon, var/high_accuracy = FALSE)
+	// isicon() is apparently quite expensive so short-circuit out early if we can.
+	if(!istext(checkstate) || isnull(checkicon) || !(isfile(checkicon) || isicon(checkicon)))
+		return FALSE
+	var/checkkey = "\ref[checkicon]"
+	var/list/check = global._icon_state_cache[checkkey]
+	if(!check)
+		check = list()
+		for(var/istate in icon_states(checkicon))
+			check[istate] = TRUE
+		global._icon_state_cache[checkkey] = check
+	. = check[checkstate]