rustdoc-search: search never type with !

This feature extends rustdoc to support the syntax that most users will
naturally attempt to use to search for diverging functions.
Part of #60485

It's already possible to do this search with `primitive:never`, but
that's not what the Rust language itself uses, so nobody will try it if
they aren't told or helped along.

tests/rustdoc-js-std/parser-returned.js

@@ -84,12 +84,12 @@ const PARSED = [
         foundElems: 1,
         original: "-> !",
         returned: [{
-            name: "!",
-            fullPath: ["!"],
+            name: "never",
+            fullPath: ["never"],
             pathWithoutLast: [],
-            pathLast: "!",
+            pathLast: "never",
             generics: [],
-            typeFilter: -1,
+            typeFilter: 15,
         }],
         userQuery: "-> !",
         error: null,