Added GitHub Action to build generated files and push them to the `generated` branch.

PiperOrigin-RevId: 438583959

.github/workflows/generate_files.yml

@@ -0,0 +1,20 @@
+name: Generate Files
+
+# After any push to the main branch, re-generate pregenerated files.
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  generate:
+    runs-on: ubuntu-20.04
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Merge generated branch with main
+        run: cd ${{ github.workspace} && (git checkout generated || git checkout -b generated) && git merge --no-edit main
+      - name: Rebuild generated CMake files
+        run: cd ${{ github.workspace }} && bazel test cmake:test_generated_files || bazel-bin/cmake/test_generated_files --fix
+      - name: Commit and push changes to generated files
+        run: cd ${{ github.workspace }} && git add -A && git diff --staged --quiet || (git commit -am "Regenerated files" && git push)

.gitignore

@@ -2,3 +2,5 @@
 obj/
 lib/
 bazel-*
+_build
+.vscode