Add ManualPermissionCheckDetector

This linter looks at methods that implement an AIDL interface.
If a given method contains a simple permission check, it suggests
moving that check to an @EnforcePermission annotation. The intent
is to keep as many permission checks as possible at a lower-level
to the service implementation, thus mitigating permission bypass
vulnerabilities.

Also rearranges some helpers/constants for reuse, and moves everything related to aidl to its own package.

Test: atest ManualPermissionCheckDetectorTest --host
Bug: 232058525
Change-Id: Ie6eaf061d74bd773742aa47f731e95e4b137f438