Fix issue with aspect ratio not applying correctly when PIP is expanded

- The current code always used the default min edge size to calculate the
  PIP bounds when the aspect ratio changes, so if a PIP app sets the aspect
  ratio in response to the an action, the bounds would be resized down
  incorrectly.
- This CL fixes the issue with current aspect ratio not being initialized
  correctly, and also ensures that SystemUI always updates the min edge
  size when expanding the PIP.

Bug: 38324839
Test: android.server.cts.ActivityManagerPinnedStackTests
Test: go/wm-smoke

Change-Id: Ida0f68b2f8f93f9bf1915dda8762a156704d4709