Added a new IRCanonicalizer pass.

Summary:
Added a new IRCanonicalizer pass which aims to transform LLVM modules into
a canonical form by reordering and renaming instructions while preserving the
same semantics. The canonicalizer makes it easier to spot semantic differences
when diffing two modules which have undergone different passes.

Presentation: https://www.youtube.com/watch?v=c9WMijSOEUg

Reviewed by: plotfi

Differential Revision: https://reviews.llvm.org/D66029