Add an MVP for policy annotations

Currently there are no users of this API, they will be added in later
CLS.

Can only represent:

* Which field is a policy.
* What type a policy has.
* The documentation of a policy.

Bug: 433951378
Bug: 434919316
Flag: android.app.admin.flags.policy_streamlining
Test: None
Change-Id: I90f431650cadb1078ae15db2c57caaf8955cf4b9