Add TheoryInference base class (#4990)

Add TheoryInference base class (#4990)

This introduces a TheoryInference base class, which is a generalization and cleaner version of the former Lemma object. This changes the name of Lemma -> SimpleTheoryLemma, and makes the callback responsible for calling the inference manager.

This PR also updates the datatypes inference manager to use the new style. This required adding some additional interfaces to TheoryInferenceManager.