R1:a11dab59b0d5

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

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