JSON editor field type.
Validates string and structured input against the field's ash_type
(:map / Ash.Type.Map accepts only objects; {:array, _} accepts only
arrays). On parse_params/2, JSON strings are decoded to native terms;
invalid JSON falls through unchanged so the validator can surface the
error message.
See MishkaGervaz.Form.Behaviours.FieldType and MishkaGervaz.Form.Types.Field.