* Extend image_tag to accept ActiveStorage's Attachments and Variants

* Flip resolve_image_source around

* Add tests for the new use-cases of image_tag

* Remove the higher-level test

* Update image_tag documentation

* Add error states into the test suite

* Re-raise polymorhic_url's NoMethodError as ArgumentError

* delegate_missing_to will raise DelegationError instead of NoMethodError