Replaces world.icon_size (and some magic numbers) with defines (#86819)

## About The Pull Request

All usages of world.icon_size in code have been replaced with new
`ICONSIZE_X`, `ICONSIZE_Y` and `ICONSIZE_ALL` defines depending on
context

Replaces some "32" magic numbers with the defines

A few bits of code have been modified to split up x/y math as well

## Why It's Good For The Game

Magic number bad, code more readable, code more flexible and I'm told
there's an access cost to doing world.icon_size so minor performance
gains

## Changelog

🆑 tonty
code: made some code relating to the world's icon size more readable
/🆑

---------

Co-authored-by: Ghom <42542238+Ghommie@users.noreply.github.com>

code/modules/tutorials/tutorial_instruction.dm

@@ -38,7 +38,7 @@
 
 	var/view = client?.view_size.getView()
 	maptext_width = view ? view_to_pixels(view)[1] : 480
-	pixel_x = (maptext_width - world.icon_size) * -0.5
+	pixel_x = (maptext_width - ICON_SIZE_X) * -0.5
 
 	change_message(message)