chore: use our own AsAny to provide &dyn Any

This removes the direct requirement to implement `as_any` and it could
be just derived.

Also implement HasDisplayHandle for dyn ActiveEventLoop + '_.

Suggested-by: daxpedda <daxpedda@gmail.com>

src/platform_impl/windows/event_loop.rs

@@ -570,10 +570,6 @@ impl RootActiveEventLoop for ActiveEventLoop {
         RootOwnedDisplayHandle { platform: OwnedDisplayHandle }
     }
 
-    fn as_any(&self) -> &dyn std::any::Any {
-        self
-    }
-
     fn rwh_06_handle(&self) -> &dyn rwh_06::HasDisplayHandle {
         self
     }