Update MSRV to Rust 1.70.0 (#3310)

* Update to Rust 1.70

* Fix renamed clippy lint

* Use let-else more

* Code cleanup

* Remove derelict Safety comments

* Enable more clippy lints

crates/eframe/src/web/web_painter_wgpu.rs

@@ -148,9 +148,7 @@ impl WebPainter for WebPainterWgpu {
     ) -> Result<(), JsValue> {
         let size_in_pixels = [self.canvas.width(), self.canvas.height()];
 
-        let render_state = if let Some(render_state) = &self.render_state {
-            render_state
-        } else {
+        let Some(render_state) = &self.render_state else {
             return Err(JsValue::from_str(
                 "Can't paint, wgpu renderer was already disposed",
             ));