Add WallpaperCropperTest

Those are unit tests for the WallpaperCropper helper methods. End-to-end
tests for the multi crop APIs will be written separately.

Flag: ACONFIG com.android.window.flags.multi_crop DEVELOPMENT
Bug: 320972046
Test: atest WallpaperCropperTest
Change-Id: I8d4cad9e0454f30c8e82369bcdc8afc57b23f672
2 files changed