ticket:9803: Add API to get number formatter from UFile

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@33101 251d0590-4201-4cf1-90de-194747b24ca1
ticket:9899: Update description for u_fgetfile and u_fgetConverter

git-svn-id: http://source.icu-project.org/repos/icu/icu/trunk/source@33102 251d0590-4201-4cf1-90de-194747b24ca1