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.

Cargo.lock

@@ -1852,9 +1852,9 @@ checksum = "b7ac824320a75a52197e8f2d787f6a38b6718bb6897a35142d749af3c0e8f4fe"
 
 [[package]]
 name = "flate2"
-version = "1.1.2"
+version = "1.1.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4a3d7db9596fecd151c5f638c0ee5d5bd487b6e0ea232e5dc96d5250f6f94b1d"
+checksum = "bfe33edd8e85a12a67454e37f8c75e730830d83e313556ab9ebf9ee7fbeb3bfb"
 dependencies = [
  "crc32fast",
  "miniz_oxide",
@@ -6278,6 +6278,7 @@ dependencies = [
  "anyhow",
  "cosmic-text",
  "etagere",
+ "flate2",
  "glam",
  "image",
  "log",