Mark extensible enums in winit-core as #[non_exhaustive]

Event, input source, error, data transfer, native key, IME request,
scroll delta and fullscreen enums can now gain variants without a
breaking change. Backends and examples get wildcard arms where they
matched exhaustively; unknown IME requests are reported as
ImeRequestError::NotSupported and unknown fullscreen modes behave
like Fullscreen::Borderless(None).

winit-orbital/src/window.rs

@@ -342,6 +342,7 @@ impl CoreWindow for Window {
             None => {
                 let _ = self.set_flag(ORBITAL_FLAG_FULLSCREEN, false);
             },
+            Some(_) => (),
         }
     }