[lib] Move conversion function out of validation utils

Summary: Changes required for fixing ENG-4670 introduce some cyclic dependencies so we need to move some things around.

Test Plan: yarn test-all, yarn eslint, yarn flow-all

Reviewers: tomek, inka, kamil, ginsu

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D8879