[llvm] Add more generic `half`/`bfloat` tests (NFC) (PR #157211)

[via llvm-commits]

beetrees wrote:

I've removed the `half` FMA test and merged `half-op.ll` into `half.ll`. BPF and DirectX have compilation failures with the extra test cases, so I've split them to have separate tests. I've also removed the `bfloat` tests, as `bfloat` already uses `TypeSoftPromoteHalf` in all cases (where `bf16` isn't a legal type) and almost all the `BAD` cases would be fixed by #156343 anyway.

https://github.com/llvm/llvm-project/pull/157211