Require TokenizerControl to always have a datasource

Summary:
Ref T4100. I can simplify the logic a bit here by moving some rendering into the datasources, but a few TokenizerControls currently don't have datasources.

Require datasources and always provide datasources.

Test Plan:

• Used previously-datasourceless controls (e.g., "Add Reviewers").
• Used normal controls.
• Manually verified that no other controls are missing datasources.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4100

Differential Revision: https://secure.phabricator.com/D12456