Update read wallpaper methods (U and above)

The following methods in WallpaperManager:
  - getDrawable()
  - getDrawable(int which)
  - peekDrawable()
  - peekDrawable(int which)
  - getFastDrawable()
  - getFastDrawable(int which)
  - peekFastDrawable()
  - peekFastDrawable(int which)
  - getWallpaperFile(int which)

Have been changed in T to return the default system wallpaper data unless the caller has the internal permission READ_WALLPAPER_INTERNAL (or MANAGE_EXTERNAL_STORAGE).

The READ_WALLPAPER_INTERNAL permission has been added in the SystemUI and shell AndroidManifest.

This CL also stops returning the cached wallpaper if an app doesn't hold
the READ_WALLPAPER_INTERNAL permission.

Test: treehugger
Test: atest CtsScopedStorageDeviceOnlyTest
Test: atest ScopedStorageHostTest
Test: atest CtsAppOpsTestCases
Test: atest CtsWallpaperTestCases
Test: atest NoWallpaperPermissionsTest
Test: atest LauncherIronwoodIntegrationTests (see
HomescreenCustomizationTests#testChangeWallpaper)
Bug: 261906287
Bug: 239784307

Change-Id: I8f90fbe78668e4e1d09188196180ca39c6b760b1