Injection token provided by controls inside a cngx-form-field (or any
other host that consumes the same contract). The form-field reads this
to discover the active control and project ARIA back onto it.
@cngx/forms/field re-exports this constant so the existing
import { CNGX_FORM_FIELD_CONTROL } from '@cngx/forms/field' import
path keeps working unchanged.