bug#50779: 28.0.50; Tab bar doesn't respond to mouse clicks

[Juri Linkov]

> Note: tested only in a Wayland session (sway) with pgtk.
>
> The tab bar doesn't respond to any mouse clicks (switching tabs by clicking
> them doesn't work, creating a new tab by clicking the "+" doesn't work,
> etc.).
> However, the tab line (tab-line-mode) does seem to work (although I only
> did minimal testing since I don't use it normally).
>
> Recipe:
> 1. emacs -Q
> 2. M-x tab-bar-mode
> 3. Click on any tab or button in the tab bar.

Looking at the logs of the branch feature/pgtk shows that the last time
it was updated from master was:

  2021-07-25 Merge branch 'master' of git.sv.gnu.org:/srv/git/emacs into 
feature/pgtk

This means the branch feature/pgtk is out of sync?  Recently we changed
how tab-bar mouse clicks are processed in master.