Auto merge of #138915 - compiler-errors:binder-tweak, r=lcnr

Instantiate binder before registering nested obligations for auto/built-in traits

Instead of turning a `Binder<Vec<Ty>>` into a bunch of higher-ranked predicates, instantiate the binder eagerly *once* and turn them into a bunch of non-higher-ranked predicates.

Right now this feels like a noop, but this `enter_forall_and_leak_universe` call would be the singular place where we could instantiate bound lifetime assumptions for coroutine witnesses... if we had them. Thus consolidating the binder instantiation here is useful if we want to fix the coroutine-auto-trait problem.

r? lcnr

Author: bors