[lib] introduce function to find deep difference between two objects

Summary:
Implement function returning objects with properties that are included in first object but not included in second one.

Flow doesn't like generic Map<K, T> while iterating over properties, so I used Object.

Depends on D7752

Test Plan: Run tests

Reviewers: michal, ashoat

Reviewed By: ashoat

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7753