4b/ Migrate TopTaskTracker to use visible running tasks from Shell

- When enable_shell_top_task_tracking is enabled, use the shell
  provided signals to keep an up-to-date running (visible) task list
  on the Launcher side, instead of managing the list via to-front
  signals from Core via TaskStackListener.  In doing so, we also
  update CachedTaskInfo to use this visible task list in preparation
  for future refactoring to use the GroupedTaskInfos directly instead.

Bug: 346588978
Flag: EXEMPT adding new flag enable_shell_top_task_tracking
Test: Build SystemUI & Launcher
Test: atest WMShellUnitTests
Change-Id: I16d515243760a17258a727e2502e35387da87589