Fix B&R for multi crop

The method findNewCropFromOldCrop was not yet used in the multi-crop
case. Use it to adjust every crop. Also modify the method slightly:
 - Make it work when the target device is wider than source device
 - Prefer adding content to the crop rather than removing some, even if
   we need to add more content on one side. In most cases we'd rather
   break symmetry one one axis than removing content (i.e. zooming)

Also, drop the LANDSCAPE crop hint in restore unless the new device has
a large screen (min width > 600 dpi). We don't really care about the
landscape crop except for tablet devices, and keeping it can lead to
difficult to explain behaviours (e.g. it may affect wallpaper position
on connected displays).

Refactor the logic a bit to mock the display and bitmap sizes to make
the crop logic easily testable (Display and DisplayManager are final).
Then, add a couple test cases. There are way too many possible B&R
combinations; so pick 15 that are realistic and cover more or less all
the logic. These tests expect exact matches but are well commented.

Flag: android.app.fix_wallpaper_crops_on_restore
Test: manual
Test: atest WallpaperBackupAgentTest
Bug: 332937943

Change-Id: I224e52d4804ff7cba993e7ceeb4c9af38c0192e0