Migrate off of the vscode.proposed.notebookDeprecated API

[mjbvz]

From microsoft/vscode#146831

Opening to track migrating off of VS Code's notebook.deprecate api proposal. This proposal is currently not on track for finalization

The suggested fix in this case is to move the output id into the custom metadata: microsoft/vscode#146831 (comment)

[DonJayamanne]

Proposal:

• Add transient metadata into outputs (upstream vscode changes)
• Add the output id into this transient property
• This output id will now be available on the client and the webview