Implement epic text-field migration Drush commands.

[ndouglas]

Description

If I'm going to do this thing, I'm going to want better control than just running drush updb repeatedly.

Goals

• Report time usage accurately, regardless of failure.
• Report peak memory usage accurately, regardless of failure.
• Give good progress updates, whether with batching or not.

Tasks

• Drush command to migrate a specific field on a specific content type.
• Drush command to rollback the migration of that specific field on that specific content type.
• Drush command to verify a migration completed successfully (how?).
• Drush command to find (if possible) fields that haven't been migrated yet.

Acceptance Criteria

• Drush commands exist in a stub form, ready to be hooked up to whatever contains the core logic (see Implement epic text-field migration core logic. #13699).