Properly check MANAGE_EXTERNAL_STORAGE for wallpaper

checkCallingOrSelfPermission is not correct for apps that get
MANAGE_EXTERNAL_STORAGE through AppOp.

Flag: EXEMPT single-CL bugfix
Bug: 341974583
Test: manual with a sample app from public bug b/360905185
Change-Id: I32b1d8fab2aa7316aa5060a6e67e83d0e6b38df0