Rollup merge of #129725 - compiler-errors:predicates-of, r=fmease

Stop using `ty::GenericPredicates` for non-predicates_of queries

`GenericPredicates` is a struct of several parts: A list of of an item's own predicates, and a parent def id (and some effects related stuff, but ignore that since it's kinda irrelevant). When instantiating these generic predicates, it calls `predicates_of` on the parent and instantiates its predicates, and appends the item's own instantiated predicates too:

acb4e8b625/compiler/rustc_middle/src/ty/generics.rs (L407-L413)

Notice how this should result in a recursive set of calls to `predicates_of`... However, `GenericPredicates` is *also* misused by a bunch of *other* queries as a convenient way of passing around a list of predicates. For these queries, we don't ever set the parent def id of the `GenericPredicates`, but if we did, then this would be very easy to mistakenly call `predicates_of` instead of some other intended parent query.

Given that footgun, and the fact that we don't ever even *use* the parent def id in the `GenericPredicates` returned from queries like `explicit_super_predicates_of`, It really has no benefit over just returning `&'tcx [(Clause<'tcx>, Span)]`.

This PR additionally opts to wrap the results of `EarlyBinder`, as we've tended to use that in the return type of these kinds of queries to properly convey that the user has params to deal with, and it also gives a convenient way of iterating over a slice of things after instantiating.

compiler/rustc_lint/src/multiple_supertrait_upcastable.rs

@@ -45,8 +45,7 @@ impl<'tcx> LateLintPass<'tcx> for MultipleSupertraitUpcastable {
             let direct_super_traits_iter = cx
                 .tcx
                 .explicit_super_predicates_of(def_id)
-                .predicates
-                .into_iter()
+                .iter_identity_copied()
                 .filter_map(|(pred, _)| pred.as_trait_clause());
             if direct_super_traits_iter.count() > 1 {
                 cx.emit_span_lint(