ui/cocoa: Override windowDidResignKey

This fixes pressed keys being stuck when the deck is clicked and the
window loses focus.

In the past, Gustavo Noronha Silva also had a patch to fix this issue
though it only ungrabs mouse and does not release keys, and depends on
another out-of-tree patch:
https://github.com/akihikodaki/qemu/pull/3/commits/e906a80147b1dc6d4f31b6a08064ef9871a2b76c



Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20230228070946.12370-1-akihiko.odaki@daynix.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>