Fixing issue with the pinned stack being cropped incorrectly.

- Pinned stacks were being treated as full screen tasks, and bounded 
  (incorrectly) to the display rect leading to negative insets.  In 
  turn, this caused the view root to have negative insets, which caused
  layout to be extended (width - (-inset)) when measured.

Test: android.server.cts.ActivityManagerPinnedStackTests
Test: #testPinnedStackOutOfBoundsInsetsNonNegative

Change-Id: I3339d982667c981a3c8ca56fb3542188de1d6714