Separate input to flag generation from hiddenAPIFlagFileInfo

Encapsulating the information needed by hidden API processing in a
struct makes it easy to add additional information in future and allows
the code to populate that struct from various different sources to be
grouped together.

Bug: 179354495
Test: m com.android.art com.android.ipsec com.android.os.statsd com.android.conscrypt
      - verify that this does not change the contents of the apex files
Change-Id: I53805737dff36a3ae87aca5aad51cf46ae1361fe