Add support for nested builders on octets fields instead of visitors

[cmebarrow]

Objective is to be able to write code like the following:

        private final SseEventFW.Builder sseEventRW = new SseEventFW.Builder();

        DataFW data = dataRW.wrap(writeBuffer, 0, writeBuffer.capacity())
            .streamId(targetId)
            .groupId(0)
            .padding(padding)
            .payload(sseEventRW)
                .data(data)
                .timestamp(timestamp)
                .id(id)
                .type(type)
                .build()
            .build();

instead of

       final Consumer<Builder> payloadMutator = timestampRequested ?
               p -> p.set(visitSseEvent(eventData, id, type, timestamp)):
               p -> p.set(visitSseEvent(eventData, id, type));

       DataFW data = dataRW.wrap(writeBuffer, 0, writeBuffer.capacity())
           .streamId(targetId)
           .groupId(0)
           .padding(padding)
           .payload(payloadMutator)
           .build();

Purpose is to avoid the use of lambdas to improve performance and make coding easier.

[cmebarrow]

This may require enhancing FlyWeight.Builder to take an optional second type parameter indicating the outer builder type to be returned from build(), or adding a parameterized variant of wrap indicating the same information.