Fix getTaskId when BubbleTaskViewListener is enabled.

When Flags.enableBubbleTaskViewListener() is enabled, the task ID is
stored in BubbleTaskViewListener rather than directly in
BubbleExpandedView's mTaskId field. This caused
BubbleExpandedView.getTaskId() to return an uninitialized task ID, which
broke onActivityRestartAttempt in the BubbleController.

The issue occurs because onActivityRestartAttempt in BubbleController
retrieves existing bubbles from BubbleData and calls Bubble.getTaskId()
on each to find matches. Bubble.getTaskId() depends on
BubbleExpandedView.getTaskId(), which was returning an uninitialized
value when the flag was enabled.

Bug: 272102927
Flag: com.android.wm.shell.enable_bubble_task_view_listener
Test: atest WMShellRobolectricTests:BubbleExpandedViewTest
Test: atest WMShellMultivalentTestsOnDevice:BubbleExpandedViewTest
Change-Id: I0648b2865f9d82f33eac3b1e38b242c7405909f3