[CS] 5/N: Move WallpaperController to WallpaperRepo.

Bug: 277762009
Bug: 277764509
Test: on fold device, set a wallpaper with and without default unfold
transition. Verify WallpaperController has the correct value.
Test: atest WallpaperRepositoryImplTest WallpaperControllerTest
Change-Id: I85321f996a18cb5f01f14087d4d8cc557bcb6237

Change-Id: I457758e223ab651ea7ba725f3f5a05f20398bf2d