[WebAssembly] Update the test for `half` (NFC) (#152832)
Replace the existing `f16` test with the version that is uses for other
architectures (typically as `half.ll`). This still covers the
conversions from the existing test, but also adds checks for most simple
ops.
Additionally, rename `half-precision.ll` to `fp-intrinsics.ll` to keep
the name similar to this test.
