[Polyglot Notebooks] Support #kernelVariable copilot chat tool

[rynoV]

Is your feature request related to a problem? Please describe.

Noted here, when using inline chat in a notebook vscode supports referencing kernel variables so the llm can access the types and values of variables in the current session.

Describe the solution you'd like

Polyglot doesn't seem to support this yet. It seems like if the kernel provided by polyglot to vscode provides certain methods, vscode will automatically support the #kernelVariable tool:

https://github.com/microsoft/vscode/blob/a4fa4eaa3e6232609e3f13c21b9f033d7a75d228/src/vs/workbench/contrib/notebook/browser/controller/chat/notebook.chat.contribution.ts#L129

I couldn't quite find where in the dotnet-interactive code a change would need to be made, but hopefully this isn't too difficult to support since the kernel variables can already be displayed