ticket:10461: Improve documentation and variable names.

git-svn-id: http://source.icu-project.org/repos/icu/icu@35109 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10461: Make RelativeDateTimeFormatter use cached, shared Numberformat and plural rules.

git-svn-id: http://source.icu-project.org/repos/icu/icu@35110 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10461: Introduce introduce cache shared object in both MeasureFormat and RelativeDateTimeFormatter.

git-svn-id: http://source.icu-project.org/repos/icu/icu@35111 251d0590-4201-4cf1-90de-194747b24ca1