Adding optional gesture direction to gesture state

Required as for live tracking of back gesture we need to know which direction user is swiping.

Bug: 369817369
Test: BackGestureRecognizerTest
Flag: com.android.systemui.shared.new_touchpad_gestures_tutorial
Change-Id: Ib83da984155b53970373e8ad110168f4be556170
6 files changed