Migrate Pip tests to new DSL format

Make sure the test can run multiple times and is stable on flame

Introduce methods to allow waitForPipWindowShow/Gone using the WindowManagerState to determine if a PIP window is active (windowingMode = PINNED), since the UiDevice method is unstable and doesn't work on TVs.

Bug: 171049720
Bug: 172321238
Bug: 171049762
Test: atest WMShellFlickerTests
Change-Id: Iade19fadeb0ba07e047eb5f64479e592920ca11e