On X11, avoid false positive key repeats

Instead of a single `bool` indicating that a key press has occured and
no key has been released since then, we store the scancode of the last
pressed key (if it is a key that repeats when held). This fixes a bug
where pressing a new key while one is already held down will be flagged
as a repeat even though it is obviously not a repeat.

src/platform_impl/linux/common/xkb_state.rs

@@ -354,7 +354,6 @@ impl KbdState {
         self.post_init(state, keymap);
     }
 
-    #[cfg(feature = "wayland")]
     pub fn key_repeats(&mut self, keycode: ffi::xkb_keycode_t) -> bool {
         unsafe { (XKBH.xkb_keymap_key_repeats)(self.xkb_keymap, keycode) == 1 }
     }