This proposal has been merged into the main ECMA-402 spec. See:
https://github.com/tc39/ecma402/commit/4257160
Note this includes some editorial and normative changes made when the
proposal was merged into the main spec, but are not in the proposal spec
itself. In particular, the following AOs were changed:
PartitionNumberRangePattern (normative)
SetNumberFormatDigitOptions (editorial)