[X86][SSE] Replace PMULDQ GetDemandedBits combine with...

[X86][SSE] Replace PMULDQ GetDemandedBits combine with SimplifyMultipleUseDemandedBits handler (Reapplied)

Recommit rL367100 which was reverted at rL367141. Until PR42777 is fixed, we no longer get the benefits of peeking through bitcasts but it does still remove a GetDemandedBits user and gives us the equivalent combines.

llvm-svn: 367172