Rollup merge of #104258 - compiler-errors:tait-closure-deduce, r=oli-obk

Deduce closure signature from a type alias `impl Trait`'s supertraits

r? `@oli-obk`

Basically pass the TAIT's bounds through the same method that we're using to deduce a signature from infer var closure bounds.

Does this need a new FCP? I see it as a logical extension of #101834, but happy to rfcbot a new one if it does.

diff --cc compiler/rustc_hir_typeck/src/closure.rs
Simple merge

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