SimplifyDemandedVectorElts for all intrinsics

SimplifyDemandedVectorElts for all intrinsics

The point is that this simplifies integration of new intrinsics into SimplifiedDemandedVectorElts, and ensures we don't miss any existing ones.

This is intended to be NFC-ish, but as seen from the diffs, can produce slightly different output.  This is due to order of transforms w/in instcombine resulting in two slightly different fixed points.  That's something we should fix, but isn't a problem w/this patch per se.

Differential Revision: https://reviews.llvm.org/D57398

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@352653 91177308-0d34-0410-b5e6-96231b3b80d8