[clang] [CIR][AArc64] Add lowering for fp16 intrinsics (step + rounding) (PR #207511)

[Andrzej Warzyński via cfe-commits]

banach-space wrote:

Sorry folks, I missed the fact that this group:
* https://arm-software.github.io/acle/neon_intrinsics/advsimd.html#markdown-toc-rounding-1

was implemented in #195021. Since there were no tests added, I have:
* Removed the implementation from this PR.
* Kept the tests (which were missing in #195021).
* Updated the summary.

If there are no fresh comments by tomorrow, I will land this. Thank you for your reviews!

https://github.com/llvm/llvm-project/pull/207511