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/egui-winit/src/window_settings.rs

@@ -137,12 +137,10 @@ fn clamp_pos_to_monitors<E>(
     let monitors = event_loop.available_monitors();
 
     // default to primary monitor, in case the correct monitor was disconnected.
-    let mut active_monitor = if let Some(active_monitor) = event_loop
+    let Some(mut active_monitor) = event_loop
         .primary_monitor()
         .or_else(|| event_loop.available_monitors().next())
-    {
-        active_monitor
-    } else {
+    else {
         return; // no monitors 🤷
     };