format currency range

UPDATE: This API is available in ICU 63.

C++:
http://icu-project.org/apiref/icu4c/numberrangeformatter_8h.html

Java:
http://icu-project.org/apiref/icu4c/classicu_1_1number_1_1NumberRangeFormatter.html

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Split from

We've gotten a request for formatting currencies with ranges, eg

$1.23-2.57

At a minimum, we need to provide access to the range pattern (eg for English, `"{0}–{1}"`). That would allow people to produce patterns like $1.23-$2.47, or with some more work, like the above.