[lib] Introduce user responder validators

Summary:
Introduce validators for the outputs of the responders in user-responders.js and for all inner types. Values for tests are generated by printing the example output values of the responders.

Depends on D7571

Test Plan: Run yarn jest

Reviewers: kamil, inka, tomek

Reviewed By: tomek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D7572