declarationExists
True when converterFqn resolves to ANY class declaration — converter or not. Lets callers distinguish "reference does not resolve" from "resolves but is not a direct MapTypeConverter subtype" when shapeOf returns null.
True when converterFqn resolves to ANY class declaration — converter or not. Lets callers distinguish "reference does not resolve" from "resolves but is not a direct MapTypeConverter subtype" when shapeOf returns null.