Allow workboard cards to be dragged again by using a larger value for infinity

Summary:
Fixes T11886. D16882 prevented workboard cards from being dragged between columns because it reduced the effective document height to almost nothing (~78px, just the menu bars).

Instead, use the larger of the document height and viewport height as "infinity".

Test Plan: Dragged columns between workboards successfully.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11886

Differential Revision: https://secure.phabricator.com/D16885