Validation should fail if a dependency is only used for its builder

[dustyholmes-wf]

A dependency, like built_value_generator, which provides a builder is ignored by the dependency check. As a result, you may place it in your dependency list without issue.

My expected outcome is that built_value_generator, when used for its builder, would fail validation if it was not lowered to a dev_dependency.

The following packages contain builders that are auto-applied or referenced in "build.yaml"
  * built_value_generator