Higher ranked trivial bounds are not checked

[leoyvens]

As can be seen in the example:

trait Trait {}
// Checked
fn foo() where i32 : Trait {}
// Not checked.
fn bar() where for<'a> fn(&'a ()) : Trait {}

In light of #2056 this will become just a lint, but still we should lint in both cases rather than just the first. This would be fixed by having well-formedness not ignore higher-ranked predicates. See #50815 for an attempted fix which resulted in too many regressions, probably for other bugs in handling higher-ranked stuff. We can try revisiting this after more chalkification.

[leoyvens]

Triage: Situation unchanged.