Merge pull request #5918 from AlbertHilb/MarkdownViewerFix

Use `MarkdownDocument` as document widget for `MarkdownViewer`.

packages/markdownviewer/src/widget.ts

@@ -312,7 +312,7 @@ export class MarkdownViewerFactory extends ABCWidgetFactory<MarkdownDocument> {
     const content = new MarkdownViewer({ context, renderer });
     content.title.iconClass = this._fileType.iconClass;
     content.title.iconLabel = this._fileType.iconLabel;
-    const widget = new DocumentWidget({ content, context });
+    const widget = new MarkdownDocument({ content, context });
 
     return widget;
   }