cocalc-jupyter: add menu options "open in jupyterlab" and "open in vs code".

[williamstein]

• This should likely be in the File menu, next to "Switch to classical notebook..."

• This should first do "Close and Halt" to avoid issues with cocalc-jupyter and jupyterlab trying to write to the same file at the same time:

• The implementation is probably easy because the URL is canonical, e.g., if the notebook is

https://cocalc.com/projects/fcbbb7d8-ee72-4f39-8db8-f35272254bf0/files/test_plot-2024-01-16-213336.ipynb

then the JupyterLab link is:

https://cocalc.com/fcbbb7d8-ee72-4f39-8db8-f35272254bf0/port/jupyterlab/lab/tree/test_plot-2024-01-16-213336.ipynb

and the Jupyter Classic link is:

https://cocalc.com/fcbbb7d8-ee72-4f39-8db8-f35272254bf0/port/jupyter/notebooks/test_plot-2024-01-16-213336.ipynb

and those servers start automatically when you visit their URL. The main issue is the first time it can take a few seconds, which can be confusing.

REQUESTED: #7261

[mforbes]

I was naturally looking for this under the Jupyter menu.

[williamstein]

The application name menu and the Help search are just somewhat copies of what macOS does:

and

All the other menus are mostly inspired by JupyterLab, where it makes sense.

[williamstein]

This is a good idea, but I'm changing the title to just JupyterLab (as classic is deprecated).

[williamstein]

And adding vscode, as vscode is uniquely good at some things (e.g., LSP support), and easy to fully support.