utils: add cast_* methods to allow more type-safe casting

Relying on just `as_any` was error prone and will become redundant in
the future, once upcasting will be stable, we also won't to impose a
restriction on to which concrete type we're casting, since casting
to a type that doesn't implement a base trait doesn't make much
sense.

Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

src/event_loop.rs

@@ -25,7 +25,7 @@ use crate::application::ApplicationHandler;
 use crate::error::{EventLoopError, RequestError};
 use crate::monitor::MonitorHandle;
 use crate::platform_impl;
-use crate::utils::AsAny;
+use crate::utils::{impl_dyn_casting, AsAny};
 use crate::window::{CustomCursor, CustomCursorSource, Theme, Window, WindowAttributes};
 
 /// Provides a way to retrieve events from the system and from the windows that were registered to
@@ -406,6 +406,8 @@ impl HasDisplayHandle for dyn ActiveEventLoop + '_ {
     }
 }
 
+impl_dyn_casting!(ActiveEventLoop);
+
 /// A proxy for the underlying display handle.
 ///
 /// The purpose of this type is to provide a cheaply cloneable handle to the underlying