ticket:10458 Add DecimalFormatPatternParser to parse pattern strings. Add code in DecimalFormat that compares the new way with the old.

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@34515 251d0590-4201-4cf1-90de-194747b24ca1
ticket:10458: Factor out parsing of pattern string into decimalformatpattern.cpp

git-svn-id: http://source.icu-project.org/repos/icu/icu/branches/tkeep@34516 251d0590-4201-4cf1-90de-194747b24ca1