[icu-design] ICU4C 61 API Proposal: Add custom error code for NumberFormatter

[Shane C. <sf...@go...>]

*Dear ICU team & users,I would like to propose the following API for: ICU
61Please provide feedback by: 2/13/2018Designated API reviewer: AndyTicket:
http://bugs.icu-project.org/trac/ticket/13577
<http://bugs.icu-project.org/trac/ticket/13577>In ICU4C, NumberFormatter
currently sets U_ILLEGAL_ARGUMENT_ERROR when the user attempts to specify
an invalid value for one of the arguments to a helper function; for
example, something like Rounder::fixedFraction(-100).  I propose adding a
new error code to UErrorCode in utypes.h for this
case:U_DIGIT_WIDTH_OUTOFBOUNDS_ERROR,  /**< The argument to a
NumberFormatter helper method was out of bounds; the bounds are usually 0
to 999. @draft ICU 61 */I will propose adding more UErrorCode values for
NumberFormatter as needed.Thanks, Shane*