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/datums/drift_handler.dm

@@ -166,7 +166,7 @@
 	if(ignore_next_glide)
 		ignore_next_glide = FALSE
 		return
-	var/glide_delay = round(world.icon_size / glide_size, 1) * world.tick_lag
+	var/glide_delay = round(ICON_SIZE_ALL / glide_size, 1) * world.tick_lag
 	drifting_loop.pause_for(glide_delay)
 	delayed = TRUE