[5/n] Fix top rounded corners in freeform

If activity bounds match parent app bounds height, don't apply rounded
corners. Freeform activities will not have visible letterboxing except
if eligible for camera compat treatment. Pillarboxing for camera compat
will not have rounded corners to ensure consistency between apps.

Round up aspect ratio calculations in desktop mode to match activity
aspect ratio calculations in core.

Flag: com.android.window.flags.exclude_caption_from_app_bounds
Bug: 388014743
Test: atest AppCompatLetterboxPolicyTest
Change-Id: I5fbc8852c00771ffa228a5a635057eee201a4269