Two API changes:

1. Add a new formula type "INSTALLER_ALLOWD_BY_MANIFEST" that evaluates to true
when installer is specified in the manifest.

This CL only adds this class without actually removing the part where we
propagate allowed installers. That will be changed in a new CL.

2. Change the AppIntegrityComponent API so that it is type-safe.

Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/integrity
Test: atest frameworks/base/core/tests/coretests/src/android/content/integrity
Bug: 148780440, 147835536
Change-Id: Icfb996b2f6de241d9790a423dd01992edaf35117