Show file size in the file browser

[jtpio]

Problem

Current the JupyterLab File Browser does not show the size of the files:

While the Classic Notebook does:

Proposed Solution

Add an option to show the file size in the file browser, similar to the one for enabling check boxes:

Additional context

Opening a new issue because searching for a similar issue with the following filters didn't yield any result: https://github.com/jupyterlab/jupyterlab/issues?q=is%3Aopen+is%3Aissue+label%3A%22tag%3AFeature+Parity%22+label%3Apkg%3Afilebrowser

Relevant for jupyter/notebook#6397