[PiP2] Assert for layer expand in flicker test

Add an assertion to ExitPipToAppViaIntentTest that checks
whether PiP layer expands with each trace.

Do this by creating a new LayerExpands AssertionTemplateWithComponent
class that can be reused for other PiP FaaS tests later.

Bug: 430819835
Flag: com.android.wm.shell.enable_pip2
Test: atest WMShellFlickerServicePipTests:ExitPipToAppViaIntentTest
Change-Id: Ife51b937cce95231ee1269df59fa2befb0cb6471