bug#35058: [PATCH] Use display-graphic-p in more cases

[Drew Adams]

This is a great description, Eli.

I hope it or similar is recorded somewhere in
code or code-related artifacts, not just in
mail threads.

It can also help users to know some of this
(the rationale).  That isn't so important now
perhaps, as things like `display-multi-font-p'
are just aliased.  But it could be more
important later.

BTW, where would the intended meaning of such
functions be recorded now?  Currently their
doc is just the doc of `display-graphic-p',
as they are aliased.  (Could/should they have
their own doc strings now, even if the behavior
is currently just `display-graphic-p'?)