LibWeb: Don't delay document "load" event for unclosed script tags

We previously had a bug where markup with unclosed script tags caused
the document load event to be delayed indefinitely. Fix this by only
marking script elements as delaying the load event once we encounter
the script end tag.

Userland/Libraries/LibWeb/HTML/HTMLScriptElement.h

@@ -42,6 +42,8 @@ public:
 
     void set_source_line_number(Badge<HTMLParser>, size_t source_line_number) { m_source_line_number = source_line_number; }
 
+    void begin_delaying_document_load_event(Badge<HTMLParser>, DOM::Document&);
+
 private:
     void prepare_script();
     void script_became_ready();