[HostStubGen] Make HSG more modularize

In preparation for adding class processing to the ravenizer tool to
apply several bytecode transformations available in the main HSG tool,
update the code base to be more modular.

- Make hoststubgen-lib self contained.
- Extract the bytecode transformation logic into its own class
  HostStubGenClassProcessor.
- Create BaseOptions to standardize commandline parsing and allow option
  inheritance to process options that can be shared across tools.
- Make hoststubgen fully a client of hoststubgen-lib to enforce
  encapsulation within the codebase.

With these changes in place, it would be easier to update ravenizer to
directly utilize HostStubGenClassProcessor in a follow-up CL.

Bug: 397498134
Flag: EXEMPT host side change only
Test: f/b/r/scripts/run-ravenwood-tests.sh
Change-Id: Ib46e322a9ddd22375b598339d36b9ed71325dc16