bug#51411: NS port cleanups

[Po Lu]

I did not notice that the thread previously titled "NS port
improvements" was moved off bug#51251 onto emacs-devel, but now that
there are concrete changes I think it would be a good opportunity to
post them on bug-gnu-emacs, per the CONTRIBUTE document.

The changes, with the generic improvements split from the changes to
font rendering are attached.

Alan raised several questions, which I answered.  I've reproduced that
part of the discussion below:

> Is there any reason to nest ns_focus? There are (according to Apple)
> performance reasons to not save the context unless you really need to.

Right now it's used in the code that clips to the exact bounds of a
string, if a string's overhangs are already drawn.

I couldn't find a cleaner way to do this, and that situation is rare, so
I think the performance problems will usually be avoided.

> I mean alt as defined by GNUstep in the quote I sent you in my last
> email. I don't think it's our job to say that GNUstep's choice of
> defaults is wrong and therefore do something that would be unexpected
> for a GNUstep user.

Well, on every other platform Meta is on the alt on the users' keyboard.
Emacs in general doesn't conform to the platform expectations WRT to key
bindings, so I think being consistent with Emacs on other platforms is
more important here.

But in the end, it's your call.  Thanks.

0002-General-improvements-to-NS-port.patch
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0001-Improve-font-display-on-NS-port.patch
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