chore: Docusaurus with webpack 5 (#500)

Summary:
Use an unreleased version of Docusaurus to test the webpack5 support works for this site, detect potential problems, and perf improvements.

See also facebook/docusaurus#4089

Pull Request resolved: #500

Reviewed By: dulinriley

Differential Revision: D28129952

Pulled By: Huxpro

fbshipit-source-id: 07942b60d5200ea6dc3a9de86844da349f700a31

doc/CrossCompilation.md

@@ -39,4 +39,4 @@ This process is currently happened in different places for different platforms:
 
 1. For Android, this happened in `hermes/android/build.gradle`
 2. For Apple platforms, this happend in `hermes/utils/build-apple-framework.sh`
-3. For Emscripten, you can find an example from the `test-emscripte` job from `hermes/.circleci/config.yml`. Also see more details at [Building with Emscripten](../emscripten)
+3. For Emscripten, you can find an example from the `test-emscripten` job from `hermes/.circleci/config.yml`. Also see more details at [Building with Emscripten](./Emscripten.md)

doc/Emscripten.md

@@ -34,7 +34,7 @@ WARNING: The old `fastcomp` backend was [removed in emscripten `2.0.0` (August 2
 Hermes now requires a two stage build proecess because the VM now contains
 Hermes bytecode which needs to be compiled by Hermes.
 
-Please follow the [Cross Compilation](../CrossCompilation) to set up a workplace
+Please follow the [Cross Compilation](./CrossCompilation.md) to set up a workplace
 and build a host hermesc at `$HERMES_WS_DIR/build_host_hermesc`.
 
 

website/package.json

@@ -12,12 +12,12 @@
     "clear": "docusaurus clear"
   },
   "dependencies": {
-    "@docusaurus/core": "^2.0.0-alpha.69",
-    "@docusaurus/preset-classic": "^2.0.0-alpha.69",
+    "@docusaurus/core": "2.0.0-alpha.75",
+    "@docusaurus/preset-classic": "2.0.0-alpha.75",
     "classnames": "^2.2.6",
     "monaco-editor": "^0.19.2",
-    "react": "^16.8.4",
-    "react-dom": "^16.8.4",
+    "react": "^17.0.2",
+    "react-dom": "^17.0.2",
     "react-monaco-editor": "^0.33.0"
   },
   "browserslist": {