LibWeb+LibWebView+WebContent: Add traverse_history_by_delta() IPC call

Author: https://github.com/kalenikaliaksandr
Commit: 0c839f0421
Pull-request: https://github.com/SerenityOS/serenity/pull/23952
Reviewed-by: https://github.com/trflynn89

Userland/Libraries/LibWebView/ViewImplementation.h

@@ -50,6 +50,7 @@ public:
     void load_html(StringView);
     void load_empty_document();
     void reload();
+    void traverse_the_history_by_delta(int delta);
 
     void zoom_in();
     void zoom_out();