feat(v2): docs versioning ❄️🔥 (#1983)

* wip: versioning

* wip again

* nits lint

* refactor metadata code so that we can have inobject properties optimization, fix typing

* remove buggy permalink code

* modify versioned docs fixture such that foo/baz only exists in v1.0.0

* refactor metadata.ts so that there is less transformon object

* more refactoring

* reduce test fixtures, refactoring

* refactoring readability

* finish metadata part

* refactor with readdir

* first pass of implementation

* fix mdx laoder

* split generated routes by version for performance & smaller bundle

* test data for demo

* refactor with set

* more tests

* typo

* fix typo

* better temporary ui

* stronger typing & docsVersion command

* add 100% test coverage for docsVersion command

* more test and delete manual docs cut

* cut 2.0.0-alpha.35 docs

* cut alpha.36 instead

* copyright

* delete versioned docs

* stronger test on metadata

* update typo

packages/docusaurus-theme-classic/src/theme/Layout/index.js

@@ -31,6 +31,7 @@ function Layout(props) {
     image,
     keywords,
     permalink,
+    version,
   } = props;
   const metaTitle = title || `${defaultTitle} · ${tagline}`;
   const metaImage = image || defaultImage;
@@ -47,6 +48,7 @@ function Layout(props) {
         {description && (
           <meta property="og:description" content={description} />
         )}
+        {version && <meta name="docsearch:version" content={version} />}
         {keywords && keywords.length && (
           <meta name="keywords" content={keywords.join(',')} />
         )}