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_extras/src/loaders/ehttp_loader.rs

@@ -33,7 +33,7 @@ impl File {
         let mime = response.content_type().map(|v| v.to_owned());
         let bytes = response.bytes.into();
 
-        Ok(File { bytes, mime })
+        Ok(Self { bytes, mime })
     }
 }