[InstCombine] reverse canonicalization of add --> or to allow more shuffle folding

This extends D48485 to allow another pair of binops (add/or) to be combined either
with or without a leading shuffle:
or X, C --> add X, C (when X and C have no common bits set)

Here, we need value tracking to determine that the 'or' can be reversed into an 'add',
and we've added general infrastructure to allow extending to other opcodes or moving 
to where other passes could use that functionality.

Differential Revision: https://reviews.llvm.org/D48662

llvm-svn: 336128