Add support for JAX-B style collections that don't have setters

[rbygrave]

Instead they have getter methods that initialise the collection like:

  public List<String> getTags() {
    if (tags == null) {
      tags = new ArrayList<>();
    }
    return tags;
  }

This change detects the case when a field does not have any matching constructor or setter, and it's a collection type (List,Set,Collection), then we assume it follows JAX-B style and the getter will initialise the collection.

We then generate code that uses the getter + addAll() ... instead of failing with the error:

"Non public field org.example.MyJaxbType tags with no matching setter or constructor?"