HackStudio: Moved code closing project from open_project to own method

Take the code which closes the current project out of open_project
method and move it into its own method.

Userland/DevTools/HackStudio/HackStudioWidget.h

@@ -104,6 +104,7 @@ private:
 
     void handle_external_file_deletion(const String& filepath);
     void stop_debugger_if_running();
+    void close_current_project();
 
     void create_open_files_view(GUI::Widget& parent);
     void create_toolbar(GUI::Widget& parent);