xdg-shell: Enable extended surface calls

Now that our qtwayland fork exports QtWayland::ExtendedSurface we
can enable this code again.

The fix was sent upstream see:

  https://codereview.qt-project.org/#/c/94056/
Click to focus without window chrome

Window chrome always eat the first click with its mouse area so we need
to give focus to windows from C++.

Stacking order algorithm is still rudimentary though.