[Form] Unable to add custom form component, without writing a new FormStructureHelper

Currently, the CoreFormStructureHelper checks if the component is in, or originates from (through the inheritance hierarchy), wcm/core/components/form.

But as soon as I make my own form component (without deriving from an existing form component), the CoreFormStructureHelper will decide: "this is not a form component" and therefore not validate my component....

The core components project does not provide a "base form field component", so I also cannot use that..

So, either:
1. Provide a base form field component, that every form field component must extend (sling:resourceSuperType)
2. Or: Relax the constraints on determining if a resource type is a "form field resource"
3. Or: Adjust the way "form field yes/no" is determined, to something that is more generic

Start by reading CoreFormStructureHelper and its check for components in or derived from wcm/core/components/form. Compare that behavior with a custom form component that has no existing form-component supertype; the work is done when a chosen approach allows such components to be recognized and validated without requiring a new FormStructureHelper.

Written by the indexing model from the issue text.