Fixed Bug 300408 - [apt] keep the order of elements in TypeElement#getEnclosedElements()

... as specified in the .java file if possible (as defined in the Javadoc).

That should fix most parts of the four-year old Bug 300408.

See https://bugs.eclipse.org/bugs/show_bug.cgi?id=300408

Would be great if that could be merged - maybe even into the 4.4 maintenance branch?