Closes #27384

I wrote #32771 before seeing #27384, and hoped that change would fix it.
It didn't because `XkbSelectNotify` wants a mask of which types of
`XkbMapNotify` to deliver, and otherwise won't send them.

I noticed quite a few events are sent just for remapping a single
keycode, so I updated the event loop to deduplicate these events (since
the handler does not attempt to apply them and instead just re-queries
keyboard info).

Also adds a missing call of `keyboard_layout_change` on `XkbMapNotify`
and `XkbNewKeyboardNotify`.

Release Notes:

- x11: Fixed handling of key remapping occurring while Zed is running
(e.g. xmodmap)