Support destructuring onCompleted callback params

[jozanza]

Checklist:

• If this PR is a new feature, please reference an issue where a consensus about the design was reached (not necessary for small changes)
• Make sure all of the significant new logic is covered by tests
• If this was a change that affects the external API used in GitHunt-React, update GitHunt-React and post a link to the PR in the discussion.

/label typescript

closes #2495

[apollo-cla]

@jozanza: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Meteor Contributor Agreement here: https://contribute.meteor.com/

[connorjacobsen]

@hwillson Anything I can do to help with this PR? It looks like the typescript definitions are broken for onComplete without this with stricter typing checks. Can't destructure objects, etc.

[hwillson]

Thanks very much for working on this @jozanza!