Rollup merge of #113698 - compiler-errors:rpitit-check, r=spastorino

Make it clearer that we're just checking for an RPITIT

Tiny nit to use `is_impl_trait_in_trait` more, to make it clearer that we're just checking whether a def-id is an RPITIT, rather than doing something meaningful with the `opt_rpitit_info`.

r? `@spastorino`

compiler/rustc_middle/src/ty/assoc.rs

@@ -96,6 +96,10 @@ impl AssocItem {
             }
         }
     }
+
+    pub fn is_impl_trait_in_trait(&self) -> bool {
+        self.opt_rpitit_info.is_some()
+    }
 }
 
 #[derive(Copy, Clone, PartialEq, Debug, HashStable, Eq, Hash, Encodable, Decodable)]