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-plugin-content-docs/src/docs.ts

@@ -14,7 +14,6 @@ import {
   normalizeUrl,
   parseMarkdownString,
   posixPath,
-  getDateTimeFormat,
 } from '@docusaurus/utils';
 import {LoadContext} from '@docusaurus/types';
 
@@ -212,7 +211,7 @@ export function processDocMetadata({
     lastUpdatedBy: lastUpdate.lastUpdatedBy,
     lastUpdatedAt: lastUpdate.lastUpdatedAt,
     formattedLastUpdatedAt: lastUpdate.lastUpdatedAt
-      ? getDateTimeFormat(i18n.currentLocale)(i18n.currentLocale).format(
+      ? new Intl.DateTimeFormat(i18n.currentLocale).format(
           lastUpdate.lastUpdatedAt * 1000,
         )
       : undefined,