Use ouroboros in FontSystem to avoid lifetime bound

Perhaps not quite what ouroboros is expected to be used for, but it's
not too bad, and avoiding the lifetime bound can be a huge help.

examples/rich-text/src/main.rs

@@ -39,7 +39,7 @@ fn main() {
         -1,
         1024 * display_scale as u32,
         768 * display_scale as u32,
-        &format!("COSMIC TEXT - {}", font_system.locale),
+        &format!("COSMIC TEXT - {}", font_system.locale()),
         &[WindowFlag::Resizable],
     )
     .unwrap();