[4/n] Apply AppCompatSafeRegionPolicy during activity launch

- Apply the safe region policy when an activity needs to be within the
  safe region and a safe region is set on the closest ancestor window.
- If the letterboxing logic is applied due to existing conditions and if
  a safe region is needed and exists, the activity will be sandboxed
within the safe region bounds.
-  If the letterboxing logic is applied due to a safe region only which is needed and exists, the safe region bounds will be used as the resolved bounds.

Bug: 380132497
Flag: com.android.window.flags.safe_region_letterboxing
Test: atest SizeCompatTests AppCompatUtilsTest AppCompatLetterboxPolicyTest
Change-Id: Ic2ee32e521b30fc4f1b07f972b172b284c01e8fa