Use Self everywhere (#3787)

This turns on the clippy lint
[`clippy::use_self`](https://rust-lang.github.io/rust-clippy/v0.0.212/index.html#use_self)
and fixes it everywhere.

crates/egui_glow/examples/pure_glow.rs

@@ -111,7 +111,7 @@ impl GlutinWindowContext {
             )
             .unwrap();
 
-        GlutinWindowContext {
+        Self {
             window,
             gl_context,
             gl_display,