Parser refactor (#55772)

Summary:
Pull Request resolved: #55772

The `main.py` increases rapidly in size. This diff refactors that into the `utils.py` and `builder.py` to form more modularized and easier to read structure.

Changelog:
[Internal]

Reviewed By: cipolleschi

Differential Revision: D94072940

fbshipit-source-id: f4b7b3c3bf4e2cf387829ced039d5645e2ad4b3e

Author: coado