Depends on gtk 3.22 for gtk_menu_popup_at_rect.

Had to rework the toolbar context menu to not execute async,
as otherwise it just closes immediately. (Basically it's same
as rhbz#1342823, except that I couldn't find a way to feed
gtk_menu_popup_at_rect with the correct timestamp).

Change-Id: I779d8803c80314d93a342f1294c7280f1adf4c98
Reviewed-on: https://gerrit.libreoffice.org/55772Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Maxim Monastirsky <momonasmon@gmail.com>