Support semantic highlighting with notebook cells

[roblourens]

See microsoft/vscode#129012

• Open a jupyter notebook
• See that semantic highlighting is not taking effect in notebook cells

I assume that this is implemented by pylance, let me know if not

[jakebailey]

We provide the semantic tokens, but I'm pretty sure bugs in the notebook middleware and concat doc break things.

See also the overarching issue on microsoft/vscode-jupyter#7877 (which is very much on our radar).

[roblourens]

Feel free to close in favor of that issue if you prefer

[jakebailey]

I think the corresponding issue in the Jupyter tracker is: microsoft/vscode-jupyter#6799

(But I don't object to having a tracking issue here for people to discover.)

[heejaechang]

this seems fixed now. it doesn't repro on latest pylance + jupyter notebook extensions.