Simplifying TouchpadGestureMonitor interface

Part of introducing gesture live progress tracking.

The main change is in TouchpadGestureMonitor and all remaining changes are just making it compile.
Next CL will rename it to GestureRecognizer.

Bug: 369817369
Test: All tests are passing
Flag: com.android.systemui.shared.new_touchpad_gestures_tutorial
Change-Id: Ia49455ed5b4fe07da1a009e35ff1177d8b40c2dc