Rollup merge of #86506 - b-naber:gen_trait_impl_inconsistent, r=jackh726

Rollup merge of #86506 - b-naber:gen_trait_impl_inconsistent, r=jackh726

Don't normalize xform_ret_ty during method candidate assembly

Fixes https://github.com/rust-lang/rust/issues/85671

Normalizing the return type of a method candidate together with the expected receiver type of the method can lead to valid method candidates being rejected during probing. Specifically in the example of the fixed issue we have a `self_ty` of the form `&A<&[Coef]>` whereas the `impl_ty` of the method would be `&A<_>`, if we normalize the projection in the return type we unify the inference variable with `Cont`, which will lead us to reject the candidate in the sup type check in `consider_probe`. Since we don't actually need the normalized return type during candidate assembly, we postpone the normalization until we consider candidates in `consider_probe`.