Removing third party notebook registration from Jupyter extension

[amunger]

The Jupyter Extension team is planning on moving the notebook creation command from the jupyter extension to core VS Code since core already has support for notebooks without requiring the extension: microsoft/vscode-jupyter#9250

What this would mean for the .NET extension:
Creating a .NET interactive notebook would no longer be available from creating a Jupyter notebook which can currently happen two ways:

1. “Jupyter: Create New Jupyter Notebook” in the command palette
   This one probably isn’t an issue since the .NET extension already has a “.NET interactive: Create New Blank Notebook” command.

2. New file… -> Jupyter Notebook -> .NET interactive
   For this, we would suggest that the .NET extension adds its own notebook type to the “New File…” menu, similar to https://github.com/microsoft/vscode/blob/32d40cf44e893e87ac33ac4f08de1e5f7fe077fc/extensions/ipynb/package.json#L56

This could possibly remove the only dependency on the Jupyter extension, unless there is another one I'm not aware of.
Let us know if there are any concerns/feedback for this change.

[amunger]

This is now live in VS code insiders and Jupyter extension pre-release

[DonJayamanne]

This will be removed in next months release 2022.9.xx