ticket:9101: fix & improve & test CollationWeights

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/markus@33798 251d0590-4201-4cf1-90de-194747b24ca1
ticket:9101: even simpler splitting of a weight range

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/markus@33799 251d0590-4201-4cf1-90de-194747b24ca1