Add a way to convert a CompositeData into a Map

CompositeDataSupport has a constructor that takes a CompositeType and a Map<String,?>. But it doesn't have the reverse option, to produce a Map<String, Object> that contains the items from the CompositeData. This would be very useful to support the creation of another CompositeData that is the same as the first except for one or two items. For example:

CompositeData cd = ...whatever...;
Map<String, Object> map = CompositeDataSupport.toMap(cd);
map.put("foo", "bar");
cd = new CompositeDataSupport(cd.getCompositeType(), map);