[lib] modify assertObjectsAreEqual to return deep differential instead of only one level keys

Summary:
Previously, when keys were the same logging wasn't saying much:

Now it shows not only missing keys but diff on each object level:

Depends on D7753

Test Plan:

1. Check if this not cause errors on equal objects
2. Check if this shows detailed information what are the differences between objects

Reviewers: tomek, michal

Reviewed By: michal

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7754