Exection Tests: Long Vector Binary Math Ops (microsoft#7696)

This PR is mostly NFC, aside from some cleanup in the
getCompilerOptionsString logic. All of the binary math ops test cases
are simply renamed from earlier work. The binary math ops issue included
two additional intrinsics: pow and step. However, upon closer
inspection, I realized we already have coverage or will have coverage
later for the relevant DXIL ops and LLVM instructions. Therefore, no new
test cases needed to be added.

Resolves microsoft#7615

Author: alsepkow