Small fixes and tweaks to PiP transition.

- Fixing case where default bounds did not account for ime height
- Ensuring that we using the animating/target bounds when calculating
  the new ime-offset bounds
- Tweaking transition interpolators and durations

Bug: 35396882
Test: android.server.cts.ActivityManagerPinnedStackTests
Change-Id: Ia22ea0008d834c47a3f26bf2e1f484c72fae8736