LibWeb: Add naive support for document.querySelectorAll()

This currently returns a JS::Array of elements matching a selector.
The more correct behavior would be to return a static NodeList, but as
we don't have NodeLists right now, that'll be a task for the future.

Libraries/LibWeb/Bindings/DocumentWrapper.h

@@ -43,6 +43,7 @@ private:
     virtual const char* class_name() const override { return "DocumentWrapper"; }
 
     static JS::Value get_element_by_id(JS::Interpreter&);
+    static JS::Value query_selector_all(JS::Interpreter&);
 };
 
 }