bug#50993: 29.0.50; Problems when dragging the mouse over the toolbar

[Eli Zaretskii]

> Date: Sun, 03 Oct 2021 20:06:13 +0800
> From:  Po Lu via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> In emacs -Q, try to extend the selection by dragging the mouse upwards
> over the tool bar.  This used to extend the selection upwards as
> expected, in Emacs 27, and Emacs 28 from April, but doesn't work anymore
> in both Emacs 28.0.60 and 29.0.50, complaining:
> 
> <tool-bar> <mouse-movement> is undefined.

This is because of commit 2e595b3: we now report mouse gestures on
tool bar and tab bar with the corresponding prefixes.  And
keyboard.c+mouse.el evidently don't like to see [tool-bar mouse-movement].

I have no idea how to fix this mess; I tried many things, but gave up
eventually.  Perhaps Stefan knows what to do here.  As a kludge, maybe
remove the prefix if the full even has no binding?  Anyway, we cannot
revert that change because it was done to support mouse wheel on the
tab bar.