Implement `ListFormat`

`ListFormat` is partially done, remaining bits are related to icu4x.

| ECMA 402 API | Trait Definition | [`rust_icu`][ri] API | `rust_icu` adaptor | [`icu4x`][icu4x] API | `icu4x` adaptor |
|----------------------|---------------------|--------------------|-------------------------|----------------|-----------|
| [`Intl.ListFormat`][lf] | ✅ | ✅ | ✅ | | |

[ecma]: https://www.ecma-international.org/publications/standards/Ecma-402.htm
[proposal]: https://github.com/unicode-org/icu4x/blob/master/proposals/pr001-ecma402.md
[collator]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Collator/Collator
[dn]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DisplayNames/DisplayNames
[dtf]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/DateTimeFormat
[locale]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Locale/Locale
[nf]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat/NumberFormat
[pr]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/PluralRules/PluralRules
[rtf]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat
[lf]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/ListFormat/ListFormat
[icu4x]: https://github.com/unicode-org/icu4x
[ri]: https://github.com/google/rust_icu