[HLSL] Revert `WaveMultiPrefixCountBits` (#239439)
Revert commit `926040bad7abaff76e07a854f9f3edb3ca490248` (#238132) after
the Fuchsia build reports failures in the Clang
`WaveMultiPrefixCountBits` test.
Resolve the merge conflicts to remove only CountBits. Keep BitAnd,
BitXor, Product, Sum, and BitOr. Restore the original inline mask check
for those operations.
Remove the CountBits builtin, its HLSL alias, its DirectX intrinsic and
operation, and its tests. This change reverses the added and removed
lines from #238132 in all 12 affected files.
Assisted by: GitHub Copilot
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 40997c2f-5aaa-41c6-8d1f-3e2e9ada315f
