[X86][SSE] Add ISD::VECTOR_SHUFFLE to faux shuffle decoding (Reapplied)

Primarily, this allows us to use the aggressive extraction mechanisms in combineExtractWithShuffle earlier and make use of UNDEF elements that may be lost during lowering.

Reapplied after rL322279 was reverted at rL322335 due to PR35918, underlying issue was fixed at rL322644.

llvm-svn: 323104