Add Intl.Locale.prototype.variants as stated in https://tc39.es/ecma402/#sec-Intl.Locale.prototype.variants and also accept "variants" in option bag in Intl.Locale consturctor as in https://tc39.es/ecma402/#sec-updatelanguageid The changes to ECMA402 is merged in https://github.com/tc39/ecma402/pull/960 and the test code in test262 are merged in in https://github.com/tc39/test262/pull/4474/
TC39 already approve for the change so it is now part of ECMA402 spec.