Rollup merge of #141658 - lolbinarycat:rustdoc-search-stability-rank-138067, r=GuillaumeGomez

rustdoc search: prefer stable items in search results

fixes https://github.com/rust-lang/rust/issues/138067

this does add a new field to the search index, but since we're only listing unstable items instead of adding a boolean flag to every item, it should only increase the search index size of sysroot crates, since those are the only ones using the `staged_api` feature, at least as far as the rust project is concerned.

tests/rustdoc-js/sort-stability.js

@@ -0,0 +1,9 @@
+const EXPECTED = [
+    {
+        'query': 'foo',
+        'others': [
+            {"path": "sort_stability::old", "name": "foo"},
+            {"path": "sort_stability::new", "name": "foo"},
+        ],
+    },
+];

tests/rustdoc-js/sort-stability.rs

@@ -0,0 +1,16 @@
+#![feature(staged_api)]
+#![stable(feature = "foo_lib", since = "1.0.0")]
+
+#[stable(feature = "old_foo", since = "1.0.1")]
+pub mod old {
+    /// Old, stable foo
+    #[stable(feature = "old_foo", since = "1.0.1")]
+    pub fn foo() {}
+}
+
+#[unstable(feature = "new_foo", issue = "none")]
+pub mod new {
+    /// New, unstable foo
+    #[unstable(feature = "new_foo", issue = "none")]
+    pub fn foo() {}
+}