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.

examples/child_window.rs

@@ -6,11 +6,11 @@ mod fill;
 fn main() -> Result<(), impl std::error::Error> {
     use std::collections::HashMap;
 
-    use raw_window_handle::HasRawWindowHandle;
     use winit::{
         dpi::{LogicalPosition, LogicalSize, Position},
         event::{ElementState, Event, KeyEvent, WindowEvent},
         event_loop::{ControlFlow, EventLoop, EventLoopWindowTarget},
+        window::raw_window_handle::HasRawWindowHandle,
         window::{Window, WindowBuilder, WindowId},
     };