Rollup merge of #118000 - compiler-errors:placeholder-ty-outlives, r=aliemjay

Make regionck care about placeholders in outlives components

Currently, we don't consider a placeholder type `!T` to be a type component when it comes to processing type-outlives obligations. This means that they are essentially treated like unit values with no sub-components, and always outlive any region. This is problematic for `non_lifetime_binders`, and even more problematic for `with_negative_coherence`, since negative coherence uses placeholders as universals.

This PR adds `Component::Placeholder` which acts much like `Component::Param`. This currently causes a regression in some non-lifetime-binders tests because `for<T> T: 'static` doesn't imply itself when processing outlives obligations, so code like this will fail:

```
fn foo() where for<T> T: 'static {
  foo() //~ fails
}
```

Since the where clause doesn't imply itself. This requires making the `MatchAgainstHigherRankedOutlives` relation smarter when it comes to binders.

r? types

compiler/rustc_hir_analysis/src/outlives/utils.rs

@@ -80,6 +80,10 @@ pub(crate) fn insert_outlives_predicate<'tcx>(
                             .or_insert(span);
                     }
 
+                    Component::Placeholder(_) => {
+                        span_bug!(span, "Should not deduce placeholder outlives component");
+                    }
+
                     Component::Alias(alias_ty) => {
                         // This would either arise from something like:
                         //