Migrate DevicePolicyManagerService to use PackageManagerLocal

Because this code runs in system server and clears calling identity
anyways, the PackageManagerLocal API is lighter weight and allows
logging failures with more specificity.

Also fixes the tests to use proper mocking of the snapshot APIs.

Bug: 241384985

Test: atest com.android.server.devicepolicy

Change-Id: Iebfdb3e9da33629ad768436c9f9d16721d7595af