Docusarus: Build validation (#1329)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1329

Add build validation for `website-next`, also adding validation that `yoga-layout/sync` may be bundled by Webpack out-of-the-box.

Reviewed By: christophpurrer

Differential Revision: D47414176

fbshipit-source-id: 9adc4f9673333f4f79c91352f445489d6da05a07

.github/actions/setup-js/action.yml

@@ -17,4 +17,3 @@ runs:
     - name: yarn install
       shell: bash
       run: yarn install --frozen-lockfile
-      working-directory: javascript

.github/workflows/validate-website.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   build:
-    name: Build
+    name: Build [Gatsby]
     runs-on: ubuntu-20.04
 
     steps:
@@ -21,3 +21,21 @@ jobs:
       - name: yarn build
         run: yarn build
         working-directory: website
+
+  build_next:
+    name: Build [Docusaurus]
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Setup
+        uses: ./.github/actions/setup-js
+
+      - name: Build Yoga
+        run: yarn build
+        working-directory: javascript
+
+      - name: Build Website
+        run: yarn build
+        working-directory: website-next