[bug] Documentation for features including a locale is incorrect

[dantman]

The documentation for Intl.PluralRules states:
Locales must be specified separately by prefixing the locale name with `Intl.PluralRules~locale`, eg `Intl.PluralRules~locale.en-GB`.

However Intl.PluralRules~locale.en-GB doesn't resolve to a valid polyfill.

This is the same for Intl.RelativeTimeFormat.~locale.* as well.

In practice none of the en subtags have features, it's only en.

[longlho]

So this depends on the polyfill. E.g Intl.PluralRules locales do not vary per region subtag but Intl.NumberFormat and friends do. Intl.RelativeTimeFormat also rolls up all regions within a lang into a single file.
The only way to know is to check like https://unpkg.com/browse/@formatjs/intl-relativetimeformat@5.2.6/dist/locale-data/

[chee]

@JakeChampion do we want to improve the documentation here, or is this working as expected?

[JakeChampion]

This is no longer true for Intl.RelativeTimeFormat -- we have the locale subtags for that feature.

I've made a pull-request to update the notes for Intl.PluralRules -- #1084