Default document widgets are different in JupyterLab and some builtin document widgets are missing. For example, in JupyterLab, if you click on a CSV file, you see a table view. In Notebook, you open it as a text editor and the table view is not available at all. We need to audit all document widgets in Notebook and test each to make sure they work and that they have the same default as Lab.

This bug was found by @ellisonbg during a bug bash.