benchmark refactor

Summary:
1. Support for index construction parameters outside of the factory string (arbitrary depth of quantizers).
2. Refactor that provides an index wrapper which is a prereq for the optimizer, which will generate indices from pre-optimized components (particularly quantizers)

Reviewed By: mdouze

Differential Revision: D51427452

fbshipit-source-id: 014d05dd798d856360f2546963e7cad64c2fcaeb

Author: algoriddle