refactor(v2): i18n cleanups / refactors (#4405)

* chore: fix various intl stuff
- remove intl-locales-supported & intl since they're deprecated and only
needed for IE11
- add new polyfills for node 12
- clean up babel intl extractor
- reset jest test timezone to UTC so it passes even for East Coast
contributor

* chore: change build to include Node 14

* docs: update i18n reqs

packages/docusaurus-utils/src/index.ts

@@ -21,7 +21,6 @@ import {
 
 // @ts-expect-error: no typedefs :s
 import resolvePathnameUnsafe from 'resolve-pathname';
-import areIntlLocalesSupported from 'intl-locales-supported';
 
 const fileHash = new Map();
 export async function generate(
@@ -634,13 +633,6 @@ export async function readDefaultCodeTranslationMessages({
   return {};
 }
 
-export function getDateTimeFormat(locale: string) {
-  return areIntlLocalesSupported([locale])
-    ? global.Intl.DateTimeFormat
-    : // eslint-disable-next-line @typescript-eslint/no-var-requires
-      require('intl').DateTimeFormat;
-}
-
 // Input: ## Some heading {#some-heading}
 // Output: {text: "## Some heading", id: "some-heading"}
 export function parseMarkdownHeadingId(