ticket:10260: Port J LocaleDisplayNamesImpl change for (->[ to C; make similar changes in uloc_getDisplayName

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@34369 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10180: document that a string trie cannot be empty

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@34380 251d0590-4201-4cf1-90de-194747b24ca1