Use per-user Shell UID for adoptShellPermissionIdentity().

Previously we were delegating the per-user Shell's permission state and
primary user Shell's app op state to the instrumentation, which is
inconsistent. We should always delegate the per-user Shell's state.

Bug: 170742504
Change-Id: I3773c2fe34f337f5790ba7d85647501a0f86522f
Test: presubmit
(cherry picked from commit e6fe4bc8)