Add aidl_hash_gen and raise an error for a frozen interface without .hash file

1. extract hash generation logic into aidl_hash_gen
2. Raise an error when an error if a frozen interface doesn't have .hash
file.

Bug: 187841663
Test: m nothing
      remove .hash and then m nothing, check if there is an error.
Test: m <aidl_interface>-freeze-api

Change-Id: If24efc44ff226cff164ad095fc642d62d0292d33
6 files changed