[deref] Implement initial set of inference rules for deref-at-point

This implements a subset of the initial set of inference rules proposed in the llvm-dev thread "RFC: Decomposing deref(N) into deref(N) + nofree". The nolias one got moved to a separate review as there was some concerns raised which require further discussion.

Differential Revision: https://reviews.llvm.org/D99135