bug#30399: 27.0.50; tooltips are broken

[martin rudalics]

> And here's the buggy behavior (starting with step 2) I see on master
> since the above commit:
>
> 0. emacs -Q
> 1. evaluate (tooltip-show "This is a test")
>     => A GTK+-themed tooltip is displayed for 10 seconds or until there
>     is an input event, then disappears.
> 2. evaluate (x-show-tip "This is a test")
>     => A GTK+-themed tooltip is displayed and remains displayed, even if
>     there are input events, until executing step 3 or repeating step 1.

This is due to a rather silly omission which should have already
defeated a feature in Emacs 26 when calling 'x-show-tip' (you've been
warned - Lisp code should call 'tooltip-show').

> 3. evaluate (let (x-gtk-use-system-tooltips)
>                (tooltip-show "This is a test"))
>     => A non-toolkit tooltip is displayed and remains displayed, even if
>     there are input events, until the end of the Emacs session (at least
>     I haven't found a way to get rid of it); however, if the GTK+-themed
>     tooltip from step 2 is still displayed when the above sexp is
>     evaluated, then after 10 (not 5) seconds the GTK+-themed tooltip
>     disappears (but the non-toolkit tooltip remains).
> 4. evaluate (let (x-gtk-use-system-tooltips)
>                (x-show-tip "This is a test"))
>     => A non-toolkit tooltip is displayed and remains displayed, even if
>     there are input events, until the end of the Emacs session AFAICT; if
>     the tooltip from step 3 is still displayed when the above sexp is
>     evaluated, it is just moved by this step but does not disappear, and
>     if the GTK+-themed tooltip from step 2 is still displayed that
>     tooltip also remains displayed (unlike in step 3).

Let-binding 'x-gtk-use-system-tooltips' is a more delicate issue.  As
a rule, options should never be let-bound but since the customizer is
always right we'll probably have to fix this as well.

Please try the attached fix.  And please test it also with the inverse
scenario

(setq x-gtk-use-system-tooltips nil)
(let ((x-gtk-use-system-tooltips t))
  (tooltip-show "Test"))

Thanks, martin

gtk-tooltip.diff
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