Add a functional test for minimizing AutoPip enabled app

This CL adds a new test scenario which minimizes the window of
the app which enters PiP automatically.

Flag: EXEMPT adding a test
Bug: 373973157
Test: atest PlatformScenarioTests:com.android.wm.shell.functional.MinimizeAutoPipAppWindowTest
Change-Id: Ic2e4b2fa744ee2febd7492bbc1da046427adb6d3