Migrate over to enabledApiProposals #18184

This is being tracked in https://github.com/microsoft/vscode-internalbacklog/issues/2461.

This will require us to update our type definitions via @types/vscode (which we should make sure is in line with our engines definition for VS Code).

Will very likely need to specify at least "languageStatus" and "notebookConcatTextDocument".

Migration guide: microsoft/vscode#136964