Add types for Intl.ListFormat

Intl.ListFormat.d.ts

// Intl.ListFormat is in stage 3, so TS doesn't include it

declare namespace Intl {
    interface ListFormatOptions {
        /** The locale matching algorithm to use. Possible values are `lookup` and `best fit`; the default is `best fit`. For information about this option, see the [Intl](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locale_negotiation) page. */
        localeMatcher?: 'lookup' | 'best fit';

        /** The format of output message. Possible values are `conjunction` that stands for `and`-based lists (default, e.g., `A, B, and C`), or `disjunction` that stands for `or`-based lists (e.g., `A, B, or C`). `unit` stands for lists of values with units (e.g., `5 pounds, 12 ounces`). */
        type?: 'conjunction' | 'disjunction' | 'unit';

        /** The length of the formatted message. Possible values are: `long` (default, e.g., `A, B, and C`); `short` (e.g., `A, B, C`), or `narrow` (e.g., `A B C`). When style is `short` or `narrow`, `unit` is the only allowed value for the type option. */
        style?: 'long' | 'narrow' | 'short';
    }

    interface FormatParts {
        type: 'element' | 'literal';
        value: string;
    }

    /**
     * The **`Intl.ListFormat()`** constructor creates [`Intl.ListFormat`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/ListFormat) objects that enable language-sensitive list formatting.
     *
     * ``` js
     * const vehicles = ['Motorcycle', 'Bus', 'Car'];
     *
     * const formatter = new Intl.ListFormat('en', { style: 'long', type: 'conjunction' });
     * console.log(formatter.format(vehicles)); // expected output: "Motorcycle, Bus, and Car"
     * const formatter2 = new Intl.ListFormat('de', { style: 'short', type: 'disjunction' });
     * console.log(formatter2.format(vehicles)); // expected output: "Motorcycle, Bus oder Car"
     * const formatter3 = new Intl.ListFormat('en', { style: 'narrow', type: 'unit' });
     * console.log(formatter3.format(vehicles)); // expected output: "Motorcycle Bus Car"
     *```
     */
    interface ListFormat {
        format(items: string[]): string;

        formatToParts(items: string[]): FormatParts[];
    }
    // Not defined in IE nor in Safari
    const ListFormat:
        | undefined
        | {
              new (
                  locales?: string | string[],
                  options?: ListFormatOptions
              ): ListFormat;
              supportedLocalesOf(
                  locales: string | string[],
                  options?: Pick<ListFormatOptions, 'localeMatcher'>
              ): string[];
          };
}