Regularize some wallpaper APIs

Specifically:

  + support clearing wallpapers, with similar permissions to setting
  + support adjusting padding, with similar permissions as defining
    wallpaper dimension hints (which behave somewhat similarly)

These two methods, previously @SystemApi, are now public API.

Bug: 62343054
Test: atest CtsPermissionTestCases:NoWallpaperPermissionsTest
Change-Id: I97061626b9da7bc3950a0ff9362ada91a2c16571
1 file changed