for purely return-type based searches, deprioritize clone-like functions

A clone-like function in a function that takes as an argument the type
that it returns.

However, functions that return a type variable are not counted as
clone-line. Because we're not unifying the whole function at once,
a function like `U -> T` would otherwise be counted as "clone-like"
because the generics will just unify with anything when done seperatly.

Co-authored-by: Michael Howell <michael@notriddle.com>

tests/rustdoc-js-std/return-based-sort.js

@@ -0,0 +1,30 @@
+// test that `clone`-like functions are sorted lower when
+// a search is based soley on return type
+
+const FILTER_CRATE = "core";
+
+const EXPECTED = [
+    {
+        'query': '-> AllocError',
+        'others': [
+            { 'path': 'core::alloc::Allocator', 'name': 'allocate' },
+            { 'path': 'core::alloc::AllocError', 'name': 'clone' },
+        ],
+    },
+    {
+        'query': 'AllocError',
+        'returned': [
+            { 'path': 'core::alloc::Allocator', 'name': 'allocate' },
+            { 'path': 'core::alloc::AllocError', 'name': 'clone' },
+         ],
+    },
+    {
+        'query': '-> &str',
+        'others': [
+            // type_name_of_val should not be consider clone-like
+            { 'path': 'core::any', 'name': 'type_name_of_val' },
+            // this returns `Option<&str>`, and thus should be sorted lower
+            { 'path': 'core::str::Split', 'name': 'next' },
+         ],
+    },
+]