ticket:10017: C++ duration formatting now code complete.

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@33699 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10017: Merge r33624 to r33699 from trunk.

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@33700 251d0590-4201-4cf1-90de-194747b24ca1