TextEditor: Use an automatic "modified" marker in the window title

This simplifies the application somewhat as we no longer need to
manually update the window title whenever the text document changes.

Userland/Applications/TextEditor/MainWidget.cpp

@@ -59,7 +59,7 @@ MainWidget::MainWidget()
 
     m_editor->on_change = [this] {
         update_preview();
-        update_title();
+        window()->set_modified(editor().document().is_modified());
     };
 
     m_page_view = *find_descendant_of_type_named<Web::OutOfProcessWebView>("webview");
@@ -605,9 +605,7 @@ void MainWidget::update_title()
         builder.append("Untitled");
     else
         builder.append(m_path);
-    if (editor().document().is_modified())
-        builder.append(" (*)");
-    builder.append(" - Text Editor");
+    builder.append("[*] - Text Editor");
     window()->set_title(builder.to_string());
 }