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-errors.js

@@ -359,6 +359,15 @@ const PARSED = [
         userQuery: "mod:a!",
         error: 'Invalid search type: macro `!` and `mod` both specified',
     },
+    {
+        query: "mod:!",
+        elems: [],
+        foundElems: 0,
+        original: "mod:!",
+        returned: [],
+        userQuery: "mod:!",
+        error: 'Invalid search type: primitive never type `!` and `mod` both specified',
+    },
     {
         query: "a!::a",
         elems: [],