"Undo cancellation" option during quick register for artifacts

Thinking about this after https://github.com/confluentinc/vscode/pull/3032

Users may accidentally "cancel" during one of the steps in the Artifact Quick Register flow, or may not understand the implications of `esc` during one of the steps.

Right now we quietly exit the entire flow if any of the quickpick steps return `undefined`, but a better user experience is to allow undo for these cancellations in a way that gets back to the state they had (with classes & function names ready to go if they had them).

Likely use a dialog that says "Are you sure you want to cancel?"