[4/N] APIs for verification policy and failure reasons

+ Define failure reason codes
+ Define policy constants
+ Removed VERIFICATION_FAILED_REASON_NETWORK_LIMITED
+ Add getter/setter for session and global policy overrides
+ Allow Shell to have VERIFICATION_AGENT permission

FLAG: android.content.pm.verification_service

BUG: 360129103
BUG: 360129657

Test: atest CtsPackageManagerTestCases:VerifierServiceTest

Change-Id: Ibfeb88ad71677c4c61476c8af6b8607c131072f6