Set closest bigger aspect ratio when restored setting doesn't exist.

Some values, like split-screen, require device display aspect ratio
to understand the actual float aspect ratio.

This change uses the restore device aspect ratio for half-screen,
this will be improved if needed to use backup device dimensions.

Flag: com.android.window.flags.backup_and_restore_for_user_aspect_ratio_settings
Fixes: 407738654
Test: atest UserAspectRatioBackupManagerTest
Test: manual
Change-Id: Ia095a7254bb502af39c07996496b8174061f5e38