Fork project form: Ship initFormField with validation directive

The following discussion from !55838 (merged) should be addressed:

• @dpisek started a discussion:

  question: This is more a question about the usage of the directive and definitely outside of the scope of this MR but I feel like initFormField could be shipped with the directive itself.

  The shape of the form object and the fields is so tightly coupled to the usage of the directive that it might make sense. As someone who had to figure out how to use this - would that make sense to you? 🤔