touchpad: Add three-finger drag support

Three-finger drag emulates a click and drag while placing three fingers on the touchpad. An option is added to activate it (`libinput_device_config_set_three_finger_drag_enabled`) and it add a new Event and State to the touchpad gestures' state machine. Refers #298 .


Signed-off-by: Ricardo Rodrigues <ricardo.e.p.rodrigues@gmail.com>
Co-authored-by: Yaroslav Fedevych <yaroslav@fedevych.name>
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vm-tablet-no-libwacom Test Suite No Libwacom
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Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1