Rollup merge of #159899 - LorrensP-2158466:generic_args_terms, r=khyperia

`GenericArgs::types` triage + possible fixes

cc [#t-types/call-for-participation > `args.types()` triage and fixes](https://rust-lang.zulipchat.com/#narrow/channel/618216-t-types.2Fcall-for-participation/topic/.60args.2Etypes.28.29.60.20triage.20and.20fixes/with/612733487)