add WguiFontSystem, remove FONT_SYSTEM singleton, custom fonts, add Light font weight

there are a few gzip-compressed ttf as for now, looks like variable fonts aren't parsed properly by cosmic_text. Not sure why. Also, we probably need to have a fallback for CJK characters in the future, or just fallback to the built-in ones in the OS.

wgui/src/event.rs

@@ -2,7 +2,6 @@ use std::{
 	any::{Any, TypeId},
 	cell::RefMut,
 	collections::HashSet,
-	ops::Deref,
 };
 
 use glam::Vec2;