Security: Provide generated java sources.

Enable generation of java sources for AIDL interfaces. This allows
enabling the @SensitiveData annotation without causing circular build
dependencies.

Also mark doc comments as @hide to prevent the interface from being
included in the SDK.

Bug: 174857732
Test: N/A
Merged-In: If00e4dfc24bf776f87c7e2b2e3f42350aa4d4379
Change-Id: If00e4dfc24bf776f87c7e2b2e3f42350aa4d4379