Warn on exhaustive exported enums

Enable clippy::exhaustive_enums in every crate so new exported enums
are either #[non_exhaustive] or explicitly allowed as a closed set.

winit-wayland/src/lib.rs

@@ -17,6 +17,8 @@
 
 #![allow(clippy::mutable_key_type)]
 
+#![warn(clippy::exhaustive_enums)]
+
 use std::ffi::c_void;
 use std::hash::BuildHasher;
 use std::ptr::NonNull;