Introduce a GitHub Actions workflow for publishing the website

This commit migrates this functionality away from the bots. Nowadays
it's possible to build and deploy the website to GitHub Pages directly
through the GitHub Actions, which provides a nice simplication of the
process. Not only does this remove the requirement to have a `gh-pages`
branch in the repository, it also avoids the complexity of having to
configure the workflow to commit to Git branches and allows us to remove
the Git committing code from the Gulpfile.

Note that deploying directly though GitHub Actions workflows needs to be
enabled in the repository settings, but this is easy and well documented
on the link below.

The following resources are relevant for this patch:

- Enabling deployment to GitHub Pages directly through GitHub Actions:
  https://docs.github.com/en/pages/getting-started-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site#publishing-with-a-custom-github-actions-workflow
- Uploading GitHub Pages artifacts example:
  https://github.com/actions/upload-pages-artifact#usage
- Deploying GitHub Pages artifacts example:
  https://github.com/actions/deploy-pages#usage

.github/workflows/publish_website.yml

@@ -0,0 +1,63 @@
+name: Publish website
+on: [push]
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Use Node.js 18 LTS
+        uses: actions/setup-node@v3
+        with:
+          node-version: '18'
+
+      - name: Install Gulp
+        run: npm install -g gulp-cli
+
+      - name: Install other dependencies
+        run: npm install
+
+      - name: Build the website
+        run: gulp web
+
+      - name: Archive the website
+        shell: sh
+        run: |
+          chmod -c -R +rX "$INPUT_PATH" | while read line; do
+            echo "::warning title=Invalid file permissions automatically fixed::$line"
+          done
+          tar \
+            --dereference --hard-dereference \
+            --directory "$INPUT_PATH" \
+            -cvf "$RUNNER_TEMP/website.tar" \
+            --exclude=.git \
+            --exclude=.github \
+            .
+        env:
+          INPUT_PATH: build/gh-pages
+
+      - name: Upload the website
+        uses: actions/upload-artifact@v3
+        with:
+          name: github-pages
+          path: ${{ runner.temp }}/website.tar
+          retention-days: 1
+          if-no-files-found: error
+
+  deploy:
+    name: Deploy
+    runs-on: ubuntu-latest
+    needs: build
+    permissions:
+      pages: write  # Required to deploy to GitHub Pages.
+      id-token: write  # Required to verify that the deployment originates from this workflow.
+
+    steps:
+      - name: Deploy the website
+        uses: actions/deploy-pages@v2

gulpfile.js

@@ -68,7 +68,6 @@ const COMMON_WEB_FILES = [
 ];
 const MOZCENTRAL_DIFF_FILE = "mozcentral.diff";
 
-const REPO = "git@github.com:mozilla/pdf.js.git";
 const DIST_REPO_URL = "https://github.com/mozilla/pdfjs-dist";
 
 const builder = require("./external/builder/builder.js");
@@ -2133,33 +2132,6 @@ gulp.task("wintersmith", function (done) {
   });
 });
 
-function ghPagesGit(done) {
-  const VERSION = getVersionJSON().version;
-  const reason = process.env.PDFJS_UPDATE_REASON;
-
-  safeSpawnSync("git", ["init"], { cwd: GH_PAGES_DIR });
-  safeSpawnSync("git", ["remote", "add", "origin", REPO], {
-    cwd: GH_PAGES_DIR,
-  });
-  safeSpawnSync("git", ["add", "-A"], { cwd: GH_PAGES_DIR });
-  safeSpawnSync(
-    "git",
-    [
-      "commit",
-      "-am",
-      "gh-pages site created via gulpfile.js script",
-      "-m",
-      "PDF.js version " + VERSION + (reason ? " - " + reason : ""),
-    ],
-    { cwd: GH_PAGES_DIR }
-  );
-  safeSpawnSync("git", ["branch", "-m", "gh-pages"], { cwd: GH_PAGES_DIR });
-
-  console.log();
-  console.log("Website built in " + GH_PAGES_DIR);
-  done();
-}
-
 gulp.task(
   "web",
   gulp.series(
@@ -2167,8 +2139,7 @@ gulp.task(
     "generic-legacy",
     "jsdoc",
     ghPagesPrepare,
-    "wintersmith",
-    ghPagesGit
+    "wintersmith"
   )
 );