feat(v2): core v2 i18n support + Docusaurus site Crowdin integration (#3325)

* docs i18n initial poc

* docs i18n initial poc

* docs i18n initial poc

* docs i18n initial poc

* crowdin-v2 attempt

* fix source

* use crowdin env variable

* try to install crowdin on netlify

* try to install crowdin on netlify

* try to use crowdin jar directly

* try to curl the crowdin jar

* add java version cmd

* try to run crowdin jar in netlify

* fix translatedDocsDirPath

* fix loadContext issue due to site baseUrl not being modified in generted config file

* real validateLocalesFile

* add locale option to deploy command

* better LocalizationFile type

* create util getPluginI18nPath

* better core localization context loading code

* More explicit VersionMetadata type for localized docs folders

* Ability to translate blog posts with Crowdin!

* blog: refactor markdown loader + report broken links + try to get linkify working better

* upgrade crowdin config to upload all docs folder files except source code related files

* try to support translated pages

* make markdown pages translation work

* add write-translations cli command template

* fix site not  reloaded with correct options

* refactor a bit the read/write of @generated/i18n.json file

* Add <Translate> + translate() API + use it on the docusaurus homepage

* watch locale translation dir

* early POC of adding babel parsing for translation extraction

* fs.stat => pathExists

* add install:fast script

* TSC: noUnusedLocals false as it's already checked  by eslint

* POC of extracting translations from source code

* minor typo

* fix extracted key to code

* initial docs extracted translations

* stable plugin translations POC

* add crowdin commands

* quickfix for i18n deployment

* POC  of themeConfig translation

* add ability to have localized site without path prefix

* sidebar typo

* refactor translation system to output multiple translation files

* translate properly  the docs plugin

* improve theme classic translation

* rework translation extractor to handle new Chrome I18n JSON format (include id/description)

* writeTranslations: allow to pass locales cli arg

* fix ThemeConfig TS issues

* fix localizePath errors

* temporary add write-translations to netlify deploy preview

* complete example of french translated folder

* update fr folder

* remove all translations from repo

* minor translation  refactors

* fix all docs-related tests

* fix blog feed tests

* fix last blog tests

* refactor i18n context a bit, extract codeTranslations in an extra generated file

* improve @generated/i18n type

* fix some i18n todos

* minor refactor

* fix logo typing issue after merge

* move i18n.json to siteConfig instead

* try to fix windows CI build

* fix config test

* attempt to fix windows non-posix path

* increase v1 minify css jest timeout due to flaky test

* proper support for localizePath on windows

* remove non-functional install:fast

* docs, fix docsDirPathLocalized

* fix Docs i18n / md linkify issues

* ensure theme-classic swizzling will use "nextjs" sources (transpiled less aggressively, to make them human readable)

* fix some snapshots

* improve themeConfig translation code

* refactor a bit getPluginI18nPath

* readTranslationFileContent => ensure files are valid, fail fast

* fix versions tests

* add extractSourceCodeAstTranslations comments/resource links

* ignore eslint: packages/docusaurus-theme-classic/lib-next/

* fix windows CI with cross-env

* crowdin ignore .DS_Store

* improve writeTranslations + add exhaustive tests for translations.ts

* remove typo

* Wire currentLocale to algolia search

* improve i18n locale error

* Add tests for translationsExtractor.ts

* better code translation extraction regarding statically evaluable code

* fix typo

* fix typo

* improve theme-classic transpilation

* refactor  +  add i18n tests

* typo

* test new utils

* add missing snapshots

* fix snapshot

* blog onBrokenMarkdownLink

* add sidebars tests

* theme-classic index should now use ES modules

* tests for theme-classic translations

* useless comment

* add more translation tests

* simplify/cleanup writeTranslations

* try to fix Netlify fr deployment

* blog: test translated md is used during feed generation

* blog: better i18n tests regarding editUrl + md translation application

* more i18n tests for docs plugin

* more i18n tests for docs plugin

* Add tests for pages i18n

* polish docusaurus build i18n logs

packages/docusaurus-plugin-content-blog/src/__tests__/index.test.ts

@@ -8,9 +8,15 @@
 import fs from 'fs-extra';
 import path from 'path';
 import pluginContentBlog from '../index';
-import {DocusaurusConfig, LoadContext} from '@docusaurus/types';
+import {DocusaurusConfig, LoadContext, I18n} from '@docusaurus/types';
 import {PluginOptionSchema} from '../pluginOptionSchema';
 
+const DefaultI18N: I18n = {
+  currentLocale: 'en',
+  locales: ['en'],
+  defaultLocale: 'en',
+};
+
 function validateAndNormalize(schema, options) {
   const {value, error} = schema.validate(options);
   if (error) {
@@ -34,6 +40,7 @@ describe('loadBlog', () => {
         siteDir,
         siteConfig,
         generatedFilesDir,
+        i18n: DefaultI18N,
       } as LoadContext,
       validateAndNormalize(PluginOptionSchema, {
         path: pluginPath,
@@ -66,26 +73,28 @@ describe('loadBlog', () => {
       tags: [],
       nextItem: {
         permalink: '/blog/2018/12/14/Happy-First-Birthday-Slash',
-        title: 'Happy 1st Birthday Slash!',
+        title: 'Happy 1st Birthday Slash! (translated)',
       },
       truncated: false,
     });
 
     expect(
-      blogPosts.find((v) => v.metadata.title === 'Happy 1st Birthday Slash!')
-        .metadata,
+      blogPosts.find(
+        (v) => v.metadata.title === 'Happy 1st Birthday Slash! (translated)',
+      ).metadata,
     ).toEqual({
       editUrl:
-        'https://github.com/facebook/docusaurus/edit/master/website-1x/blog/2018-12-14-Happy-First-Birthday-Slash.md',
+        'https://github.com/facebook/docusaurus/edit/master/website-1x/i18n/en/docusaurus-plugin-content-blog/2018-12-14-Happy-First-Birthday-Slash.md',
       permalink: '/blog/2018/12/14/Happy-First-Birthday-Slash',
-      readingTime: 0.01,
+      readingTime: 0.015,
       source: path.join(
         '@site',
-        pluginPath,
+        // pluginPath,
+        path.join('i18n', 'en', 'docusaurus-plugin-content-blog'),
         '2018-12-14-Happy-First-Birthday-Slash.md',
       ),
-      title: 'Happy 1st Birthday Slash!',
-      description: `pattern name`,
+      title: 'Happy 1st Birthday Slash! (translated)',
+      description: `Happy birthday! (translated)`,
       date: new Date('2018-12-14'),
       tags: [],
       prevItem: {