(refactor-input-source-to-thunk-4) Add checks to catch errors when new source types are added

Summary:
For cases where we don't capture behavior differences in polymorphic methods, adding
invariants to ensure that we don't miss anything when source types are added.

Test Plan: BK

Reviewers: sandyryza, alangenfeld, yuhan

Reviewed By: alangenfeld

Differential Revision: https://dagster.phacility.com/D5316