RE: Fix some tooltip related problems

[Drew Adams]

>  > Can we let Lisp code (and so users too)
>  > decide, here or there, which kind of tooltip to use
>  > (heavyweight "Emacs" or lightweight "system")?
> 
> The majority of users (namely those with a GTK build) can.  Lucid and
> Motif users can't because these toolkits don't support tooltips.  I
> doubt that anyone has the time to set up tooltip controls on Windows.

Dunno what that means.

1. Can users with a GTK build today use Lisp code that decides
which to use in any given (Lisp) context?  How is that done
in Lisp?

2. What do you mean by "set up tooltip controls" on Windows?
Today, on Windows you can at least use faces in tooltips.
(Dunno about using images, but I'm guessing that's OK too.)

But perhaps you mean that on Windows there are _only_
"Emacs" tooltips, not "system" tooltips?  From my point of
view that's not a problem - flexible beats inflexible.  You
say that tooltips on Windows are "heavyweight" and "incur
an entire GC cycle", but I've never noticed any performance
problem with them - on Emacs 20 through 26.