[X86][SSE] Improved blend+zero target shuffle combining to use combined shuffle mask...

[X86][SSE] Improved blend+zero target shuffle combining to use combined shuffle mask directly

We currently only combine to blend+zero if the target value type has 8 elements or less, but this was missing a lot of cases where the combined mask had been widened.

This change makes it so we use the combined mask to determine the blend value type, allowing us to catch more widened cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272003 91177308-0d34-0410-b5e6-96231b3b80d8