Eat right-click, etc., on autocomplete suggestion menu

Summary:
Ref T10163. If you right-click the suggestion menu, just eat it. I don't think we can really choose a different behavior reasonably, or that users have any reason to do this.

I'm leaving "clicking the header dismisses it", I think that behavior is fine and reasonable.

Test Plan: Control-clicked a suggestion menu, didn't trigger a suggestion.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10163

Differential Revision: https://secure.phabricator.com/D15042