This is the normal standard way in C, C++ as well as Java and there's no
longer any reason for ICU to be different. The various internal macros
providing custom boolean constants can all be deleted and code as well
as documentation can be updated to use lowercase true/false everywhere.
- Adds additional logic to NumberStringBuilder.
- Extends logic of number::impl::Field type.
- Adds tests for RBNF support.
- Adds tests from ftang's original PR.
- Wires up FormattedNumber[Range] in applicable languages.
- Adds new header files and tests, with minor cleanup to old tests.
- Adds code to guarantee terminating NUL in FormattedNumber[Range].
- Cleanup of API docs for inherited methods in FormattedNumber[Range].
