Add flicker test for pinch out pip screen resizing

Create a helper class for injecting a pinching gesture
and use it pinch out to a pip window in a flicker test.
Make pip window area increases during the animation.

Test: atest WMShellFlickerTests:ExpandPipOnPinchOpenTest

Bug: 178407318
Change-Id: I0e3dc3d78cdcafcf1dff380d76d1bea4cf629f65