Allow Product migration to set a specific revision_uid

When migrating products into Drupal Commerce, it is impossible to set a revision_uid to anything other than the uid of the user running the migration. The ability to set revision_uid would be useful in migrations that wish to preserve previous revision history from the original commerce site. The ability to set revision_uid during migration exists for basic node migrations (see MigrateDestinationNode's insert() method). A patch has been submitted that replicates this behavior, using the same method as applied to nodes, but for Commerce product migrations.

This issue was first posted to the Drupal Commerce project because its focus was on the commerce_product entity controller, but has been moved to Commerce Migrate because the proposed solution is applied to the Commerce Migrate code base, specifically the MigrateDestinationCommerceProduct import() method, to mirror the approach to the problem in MigrateDestinationNode's insert() method.