ticket:9101: adapt to new UInitOnce, get branch to build & pass tests again

git-svn-id: http://source.icu-project.org/repos/icu/icu@34484 251d0590-4201-4cf1-90de-194747b24ca1
ticket:9101: cross-update old & new RBC header versions

git-svn-id: http://source.icu-project.org/repos/icu/icu@34485 251d0590-4201-4cf1-90de-194747b24ca1
ticket:9101: latest UCA 6.3-based data

git-svn-id: http://source.icu-project.org/repos/icu/icu@34486 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10446: late ibmi fixes to fix regression in r34369


git-svn-id: http://source.icu-project.org/repos/icu/icu@34487 251d0590-4201-4cf1-90de-194747b24ca1