backends/x11: Support input-synaptics, if present.
Add support for configuring the Xorg synaptics touchpad driver.
Turns out it's very simple to support both libinput and synaptics
simultaneously, both under the heading of XI2.
Bug-Ubuntu: https://launchpad.net/bugs/
1686081
Forwarded: https://gitlab.gnome.org/GNOME/mutter/merge_requests/37
Last-Update: 2018-03-16
Gbp-Pq: Name synaptics-support.patch