ui/cocoa: Fix window clipping on macOS 14

ui/cocoa: Fix window clipping on macOS 14

macOS Sonoma changes the NSView.clipsToBounds to false by default
where it was true in earlier version of macOS. This causes the window
contents to be occluded by the frame at the top of the window. This
fixes the issue by conditionally compiling the clipping on Sonoma to
true. NSView only exposes the clipToBounds in macOS 14 and so has
to be fixed via conditional compilation.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1994
Signed-off-by: David Parsons <dave@daveparsons.net>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-ID: <20240224140620.39200-1-dave@daveparsons.net>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>