Add basic trait impls for f16 and f128

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

Fixes <https://github.com/rust-lang/rust/issues/123074>

library/core/src/lib.rs

@@ -229,6 +229,8 @@
 #![feature(doc_notable_trait)]
 #![feature(effects)]
 #![feature(extern_types)]
+#![feature(f128)]
+#![feature(f16)]
 #![feature(freeze_impls)]
 #![feature(fundamental)]
 #![feature(generic_arg_infer)]