Reexport raw-window-handle in window module

We use raw-window-handle extensive in the public API as well as we
force the users to use it to get some essential data for interop, thus
reexport it.

Fixes: #2913.

src/window.rs

@@ -18,6 +18,9 @@ pub use crate::icon::{BadIcon, Icon};
 #[doc(inline)]
 pub use cursor_icon::{CursorIcon, ParseError as CursorIconParseError};
 
+#[doc(inline)]
+pub use raw_window_handle;
+
 /// Represents a window.
 ///
 /// # Example