Refactoring tests to use reusable set of touchpad gestures

1. Moving all gestures creation to TouchpadGestureBuilder for easier gesture builder and less dependency on MotionEvent. See usages in BackGestureMonitorTest.
2. Adding test for TouchpadGestureBuilder - even though it's only used in tests now it contains important events logic
3. Changing how TouchpadGestureHandler is created - now it takes gestureMonitor as direct dependency instead of creating it.

Bug: 346579074
Test: TouchpadGestureBuilderTest
Test: BackGestureMonitorTest
Flag: com.android.systemui.shared.new_touchpad_gestures_tutorial
Change-Id: I8f999a28c3217b14d72ad3619885948dab11dcfe