Extract BubbleTaskStackListener from BubbleController.

This change extracts the task stack listener into a dedicated class to
prepare for handling bubbled tasks transitioning to fullscreen. The new
BubbleTaskStackListener class provides a more flexible structure for
managing complex bubble task interactions.

Bug: 388630258
Bug: 387193964
Flag: EXEMPT refactor
Test: atest WMShellRobolectricTests:BubbleControllerTest
Test: atest WMShellRobolectricTests:BubbleTaskStackListenerTest
Test: atest WMShellMultivalentTestsOnDevice:BubbleControllerTest
Test: atest WMShellMultivalentTestsOnDevice:BubbleTaskStackListenerTest
Change-Id: Iee55d4ed056bc3680e7876da9187ec1a749f2a43