ticket:9101: add BUILDER_DATA_TAG rather than overloading CONTRACTION_TAG; add CollationIterator subclass for data builder, replaces the builder-specific collation algorithm implementation

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/markus@34717 251d0590-4201-4cf1-90de-194747b24ca1