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/monitor.rs

@@ -12,7 +12,7 @@ use std::ops::Deref;
 use std::sync::Arc;
 
 use crate::dpi::{PhysicalPosition, PhysicalSize};
-use crate::utils::AsAny;
+use crate::utils::{impl_dyn_casting, AsAny};
 
 /// Handle to a monitor.
 ///
@@ -148,6 +148,8 @@ impl PartialEq for dyn MonitorHandleProvider + '_ {
 
 impl Eq for dyn MonitorHandleProvider + '_ {}
 
+impl_dyn_casting!(MonitorHandleProvider);
+
 /// Describes a fullscreen video mode of a monitor.
 ///
 /// Can be acquired with [`MonitorHandleProvider::video_modes`].