Add tap-button-map and tap-drag-lock touchpad settings to be handled by mutter
Gnome now misses two libinput touchpad settings:
- tap button mapping
- tap dragging lock
This commit adds two new keys into gsettings database to be handled by mutter in order to change those options.
Already tested on my system with a modified version on mutter. It's working on both X11 and Wayland.