Tightening up rotation behavior for PIP (1/3)

- Defer getting the default bounds until after the task has been reparented
  to the pinned stack
- Also move pinned stack-related methods into pinned stack window
  controller and listener

Bug: 36879891
Test: android.server.cts.ActivityManagerPinnedStackTests

Change-Id: Ib2bd81ad9e2a3829b556177010f39c7512ba35bf