Properly implement Debug for Window and EventLoop types (#3297)

For EventLoop, EventLoopBuilder, EventLoopProxy and by requiring it as
a supertrait of Window and ActiveEventLoop.

It is especially useful for user to be able to know that Window is Debug.

src/platform_impl/linux/wayland/window/mod.rs

@@ -34,6 +34,7 @@ pub(crate) mod state;
 pub use state::WindowState;
 
 /// The Wayland window.
+#[derive(Debug)]
 pub struct Window {
     /// Reference to the underlying SCTK window.
     window: SctkWindow,