ticket:9104: Some minor updates in the CollationElementIterator API doc, including setOffset()/setText() are OK between next()/previous() in addition to reset(). Removing class name prefix in the updated section to improve the readability (doxygen still produces links without class prefix).

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@33551 251d0590-4201-4cf1-90de-194747b24ca1