feat: Deploy GH pages with screen reader experiment (#689)

Fixes #686

This updates the GH pages workflow to:
- Automatically deploy with changes to both `main` and `add-screen-reader-support-experimental` (the screen reader experimental branch--see RaspberryPiFoundation/blockly#9283).
- Upload the screen reader version of the playground to a new `/screenreader` subdirectory in the plugin repo's GitHub pages deployment.

This will approximately double the amount of time needed for the GH pages deployment since it requires building two distinct copies of core Blockly and the plugin (tip-of-tree versions and the screen reader experimentation versions).

Conveniently, this will act as a fast way to see screen reader changes since they will go live a few minutes after a change to the plugin. Unfortunately, that does not reciprocate for changes to core Blockly (where most of the screen reader changes will actually occur), so oftentimes a manual run of the workflow will be needed (which should suffice in those cases).

Note that this needs to be approached in this way (building and uploading both projects for changes to either branch) since the action being used for deployment doesn't support partial deployment. See: actions/deploy-pages#349.

Author: BenHenning

.github/workflows/pages.yml

@@ -2,14 +2,16 @@
 name: Deploy static content to Pages
 
 on:
-  # Runs on pushes targeting the default branch
+  # Runs on pushes targeting the default and experimentation branches.
   push:
-    branches: ['main']
+    branches:
+      - main
+      - add-screen-reader-support-experimental
 
-  # Allows you to run this workflow manually from the Actions tab
+  # Allows the workflow to be manually run from the Actions tab.
   workflow_dispatch:
 
-# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
+# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages.
 permissions:
   contents: read
   pages: write
@@ -26,45 +28,77 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout blockly
+      - name: Checkout tip-of-tree core Blockly
         uses: actions/checkout@v4
         with:
           path: blockly
           repository: google/blockly
           ref: develop
 
-      - name: Checkout blockly-keyboard-experimentation
+      - name: Checkout add-screen-reader-support-experimental core Blockly
+        uses: actions/checkout@v4
+        with:
+          path: blockly-add-screen-reader-support-experimental
+          repository: google/blockly
+          ref: add-screen-reader-support-experimental
+
+      - name: Checkout tip-of-tree blockly-keyboard-experimentation
         uses: actions/checkout@v4
         with:
           path: blockly-keyboard-experimentation
 
+      - name: Checkout add-screen-reader-support-experimental blockly-keyboard-experimentation
+        uses: actions/checkout@v4
+        with:
+          path: blockly-keyboard-experimentation-add-screen-reader-support-experimental
+          ref: add-screen-reader-support-experimental
+
       - name: Setup Node
         uses: actions/setup-node@v4
         with:
           node-version: 20.x
 
-      - name: Build blockly
+      - name: Build tip-of-tree core Blockly
         run: |
           cd blockly
           npm ci
           npm run package
           cd dist
           npm link
-          cd ../..
 
-      - name: Build blockly-keyboard-experimentation
+      - name: Build tip-of-tree blockly-keyboard-experimentation
         run: |
           cd blockly-keyboard-experimentation
           npm ci
           npm link blockly
           npm run ghpages
-          cd ..
+          mkdir ../ghpages
+          cp -r build/* ../ghpages/
+
+      - name: Build add-screen-reader-support-experimental core Blockly
+        run: |
+          cd blockly/dist
+          npm unlink -g
+          cd ../../blockly-add-screen-reader-support-experimental
+          npm ci
+          npm run package
+          cd dist
+          npm link
+
+      - name: Build add-screen-reader-support-experimental blockly-keyboard-experimentation
+        run: |
+          cd blockly-keyboard-experimentation-add-screen-reader-support-experimental
+          npm ci
+          npm link blockly
+          npm run ghpages
+          mkdir ../ghpages/screenreader
+          cp -r build/* ../ghpages/screenreader/
 
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3
         with:
-          # Upload build folder
-          path: './blockly-keyboard-experimentation/build'
+          # Upload configured GH pages site files.
+          path: './ghpages'
 
   deploy:
     environment: