TGUI list conversions + bug fixes (#63354)

About The Pull Request

    Converts more inputs to TGUI. Possibly all user-facing input lists in the game.
    Did any surrounding text/number inputs as well
    Added null choice support so users can press cancel.
    Added some misc TGUI input fixes
    Fixed custom vendors while I was there

I refactored a lot of code while just poking around.
Primarily, usage of .len in files where I was already working on lists.
Some code was just awful - look at guardian.dm and its non use of early returns
If there are any disputes, I can revert it just fine, those changes are not integral to the PR.
Why It's Good For The Game

Fixes #63629
Fixes #63307
Fixes custom vendors /again/
Text input is more performant.
Part of a long series of TGUI conversion to make the game more visually appealing
Changelog

cl
refactor: The majority of user facing input lists have been converted to TGUI.
refactor: Tgui text inputs now scale with entered input.
fix: Many inputs now properly accept cancelling out of the menu.
fix: Fixes an edge case where users could not press enter on number inputs.
fix: Custom vendor bluescreen.
fix: You can now press ENTER on text inputs without an entry to cancel.
/cl

code/modules/mob/transform_procs.dm

@@ -71,12 +71,12 @@
 				landmark_loc += sloc.loc
 				break
 			landmark_loc += sloc.loc
-		if(!landmark_loc.len)
+		if(!length(landmark_loc))
 			to_chat(src, "Oh god sorry we can't find an unoccupied AI spawn location, so we're spawning you on top of someone.")
 			for(var/obj/effect/landmark/start/ai/sloc in GLOB.landmarks_list)
 				landmark_loc += sloc.loc
 
-	if(!landmark_loc.len)
+	if(!length(landmark_loc))
 		message_admins("Could not find ai landmark for [src]. Yell at a mapper! We are spawning them at their current location.")
 		landmark_loc += loc
 
@@ -305,7 +305,8 @@
 
 	var/list/mobtypes = typesof(/mob/living/simple_animal)
 	var/mobpath = tgui_input_list(usr, "Which type of mob should [src] turn into?", "Choose a type", sort_list(mobtypes, /proc/cmp_typepaths_asc))
-
+	if(isnull(mobpath))
+		return
 	if(!safe_animal(mobpath))
 		to_chat(usr, span_danger("Sorry but this mob type is currently unavailable."))
 		return
@@ -338,7 +339,8 @@
 
 	var/list/mobtypes = typesof(/mob/living/simple_animal)
 	var/mobpath = tgui_input_list(usr, "Which type of mob should [src] turn into?", "Choose a type", sort_list(mobtypes, /proc/cmp_typepaths_asc))
-
+	if(isnull(mobpath))
+		return
 	if(!safe_animal(mobpath))
 		to_chat(usr, span_danger("Sorry but this mob type is currently unavailable."))
 		return