Automerge: [msan][NFCI] Add avx512fp16-{arith-intrinsics, arith-vl-intrinsics, intrinsics} tests (#136260)

Forked from llvm/test/CodeGen/X86/avx512fp16-{arith-intrinsics,
arith-vl-intrinsics, intrinsics}.ll

The tests show that many instructions are handled suboptimally or
heuristically, but this commit message is too narrow to contain them.

Author: thurstond