Migrate off of the concat text document API proposal

[mjbvz]

👋 Hi, I work on APIs for VS Code

The VS Code Dot Net Interactive notebooks extension currently has access to the concatTextDocument api proposal. We do not plan to finalize this proposal and instead would like to remove to simplify our code. See microsoft/vscode#146781 for details

From a quick search through this repo, I don't think this extension is using ConcatTextDocument but please confirm this and let me know when we can safely remove Dot Net Interactive from the list of this api's consumers

[jonsequitur]

@brettfo Could you please confirm?

[brettfo]

Confirmed, we don't use the concat text document APIs.

@mjbvz you can remove us from the list.

[mjbvz]

Thanks for confirming! Will be removed in the next insiders build