Fix some more `non_lifetime_binders` stuff with higher-ranked trait bounds 1. When assembling candidates for `for<T> T: Sized`, we can't ICE because the self-type is a bound type. 2. Fix an issue where, when canonicalizing in non-universe preserving mode, we don't actually set the universe for placeholders to the root even though we do the same for region vars. 3. Make `Placeholder("T")` format like `T` in error messages. Fixes #108180 Fixes #108182 r? types
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