ICU formatRange output inconsistent with README about proposal-intl-numberformat-v3

[sffc]

I think this is already covered by the spec. It says:

The CollapseNumberRange abstract operation modifies result, which must be a List of Record values as described in PartitionNumberRangePattern, by removing redundant information, and returns the resulting List. The algorithm is implementation dependent, but it must not introduce ambiguity: the resulting string after modification should be unique for all pairs x and y.

For example, an implementation may choose to remove the currency symbol following the range separator, to produce "$3–5" instead of "$3–$5".

Returning result unmodified is guaranteed to be a correct implementation of CollapseNumberRange.

https://tc39.es/proposal-intl-numberformat-v3/out/numberformat/diff.html#sec-collapsenumberrange

The algorithm for collapsing is implementation- and locale-dependent.

So therefore, the only "bug" is updating the README.