Auto merge of #123085 - tgross35:f16-f128-step4.0-libs-basic-impls, r=Amanieu

Add basic trait impls for `f16` and `f128`

Split off part of <rust-lang/rust#122470> so the compiler doesn't ICE because it expects primitives to have some minimal traits.

Fixes <rust-lang/rust#123074>

Author: bors