[AVX-512] Remove masked vector extract builtins and replace with native shufflevector...

[AVX-512] Remove masked vector extract builtins and replace with native shufflevectors and selects.

Unfortunately, the backend currently doesn't fold masks into the instructions correctly when they come from these shufflevectors. I'll work on that in a future commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@285540 91177308-0d34-0410-b5e6-96231b3b80d8