Auto merge of #79945 - jackh726:existential_trait_ref, r=nikomatsakis

Move binder for dyn to each list item

This essentially changes `ty::Binder<&'tcx List<ExistentialTraitRef>>` to `&'tcx List<ty::Binder<ExistentialTraitRef>>`.

This is a first step in moving the `dyn Trait` representation closer to Chalk, which we've talked about in `@rust-lang/wg-traits.`

r? `@nikomatsakis`

diff --cc compiler/rustc_middle/src/ty/codec.rs
Simple merge

diff --cc compiler/rustc_middle/src/ty/context.rs
Simple merge

diff --cc compiler/rustc_middle/src/ty/sty.rs
Simple merge

diff --cc compiler/rustc_trait_selection/src/traits/select/confirmation.rs
Simple merge

diff --cc compiler/rustc_typeck/src/check/method/suggest.rs
Simple merge