Issue #3291147 by phenaproxima, tedbow, effulgentsia, heddn: Successfully applying an update puts the remainder of the request into an unreliable state

Issue #3271078 by phenaproxima, tedbow: Tests make requests to updates.drupal.org instead of test fixtures sometimes

Issue #3259228 by phenaproxima, tedbow: Add functional test coverage of Stage::require() to ensure only the correct dependencies are updated

This reverts commit a941773c.

Issue #3244412 by phenaproxima, tedbow: During updates, dev dependencies are moved into production dependencies

Issue #3233587 by phenaproxima, tedbow: Create a build test that tests calling API as cleanly as possible