[32/n] Fix Insets for Letterbox in Shell

Each AppCompatLetterboxPolicyState implementation contains
the information related to the letterbox surfaces bounds.
The letterbox surfaces bounds information was missing in
case of the Letterbox implmentation in shell so the
logic related to status bar opacity was broken when the
flag was enabled.

The common logic to understand if the letterbox surfaces
overlap the bar has now been moved to AppCompatLetterboxUtils.

Flag: com.android.window.flags.app_compat_refactoring
Bug: 407731267
Test: atest WmTests:AppCompatLetterboxUtilsTest
Test: atest WmTests:SizeCompatTests

Change-Id: Ibe0a4460886c17c1dd57a2d6de16f53c77ddf730