bug#44973: Add a macOS global hotkey function

[Eli Zaretskii]

> From: j@mremus.net
> Date: Sun, 3 Jan 2021 21:13:47 -0800
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, 44973@debbugs.gnu.org
> 
> I used w32-register-hot-key as an example of another instance where emacs 
> added
> an OS-specific feature in order to provide a consistent user experience across
> platforms.

w32-register-hot-key allows a consistent UX across platforms
_inside_Emacs_.  Your changes, AFAIU, aims at using Emacs as a way to
work around problems in the OS WM, not in Emacs running on that OS.

So I'm still not sure we should install this.

Lars, do you have an opinion on this?