[MemProf] Add memprof metadata related analysis utilities

Adds a number of utilities that are used to help create and update
memprof related metadata. These will be used during profile matching
and annotation, as well as by the inliner when updating the metadata.
Also adds unit tests for the utilities.

See also related RFCs:
RFC: Sanitizer-based Heap Profiler [1]
RFC: A binary serialization format for MemProf [2]
RFC: IR metadata format for MemProf [3]
(Note that the IR metadata format has changed from the RFC during
implementation, as described in the preceeding patch adding the basic
metadata and verification support.)

Depends on D128141.

Differential Revision: https://reviews.llvm.org/D128854