Rollup merge of #161750 - RalfJung:abi-check-msg, r=folkertdev

vector ABI check: reword so it makes more sense for non-obviously-vector types

Talking about "SIMD vector type `Complex<f16>`" would be a bit confusing. So instead we talk about "the function has type `$TYPE` in its signature, which is passed in SIMD vector registers".

r? @folkertdev