Re-add migrator-comment and major-version-check workflows (#11921)

Re-add the following workflows:
- #8733
- #8997

.github/workflows/major-version-check.yml

@@ -0,0 +1,46 @@
+name: Major version in changeset
+
+on:
+  pull_request:
+    branches:
+      - main
+    types:
+      - labeled
+      - unlabeled
+      - opened
+      - synchronize
+      - reopened
+
+jobs:
+  check-changesets:
+    if: |
+      !contains(github.event.pull_request.labels.*.name, '🤖Skip Major Check')
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Fetch all branches
+        run: git fetch --all
+
+      - name: Checkout the feature branch
+        run: git checkout "$GITHUB_HEAD_REF" --
+
+      - name: Check major versions in changeset entries
+        run: |
+          commits="origin/$GITHUB_BASE_REF...origin/$GITHUB_HEAD_REF"
+          changeset_files=$(git diff --name-only --diff-filter=d "$commits" -- ".changeset/*.md")
+
+          if [[ -z "$changeset_files" ]]; then
+            echo "No changeset files detected"
+            exit 0
+          fi
+
+          if ! echo "$changeset_files" | xargs grep -qE "^\s*[\"'].*?[\"']\s*:\s*major\s*$"; then
+            echo "No major version upgrade detected"
+            exit 0
+          else
+            echo "This PR contains a major version upgrade which is only used for breaking changes."
+            echo "If you are sure you want to perform this action, please add the '🤖Skip Major Check' label"
+            exit 1
+          fi

.github/workflows/migrator-comment.yml

@@ -0,0 +1,52 @@
+name: Migrator comment in diff
+
+on:
+  pull_request:
+    types:
+      - labeled
+      - unlabeled
+      - opened
+      - synchronize
+      - reopened
+
+env:
+  COMMENT: 'generated by polaris-migrator DO NOT COPY'
+
+jobs:
+  check-diff:
+    if: |
+      !contains(github.event.pull_request.labels.*.name, '🤖Skip Comment Check')
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Fetch all branches
+        run: git fetch --all
+
+      - name: Checkout the feature branch
+        run: git checkout "$GITHUB_HEAD_REF" --
+
+      - name: Check for generic migrator comment in diff
+        run: |
+          commits="origin/$GITHUB_BASE_REF...origin/$GITHUB_HEAD_REF"
+          files=$(git diff --name-only --diff-filter=d "$commits" -- "*.scss")
+
+          if [ -n "$files" ]; then
+            echo "SCSS files where modified."
+            echo "$files"
+          else
+            echo "No SCSS files where modified."
+            exit 0
+          fi
+
+          filesWithComment=$(git diff --unified=0 --diff-filter=d "$commits" -- $(echo $files) | grep "^\+.*$COMMENT" || true)
+
+          if [ -n "$filesWithComment" ]; then
+            echo "A migrator comment '$COMMENT' was added to a SCSS file in this PR."
+            echo "Please provide a description for any Stylelint disable comments."
+            echo "If this is not applicable, you can add the '🤖Skip Comment Check' label to this PR."
+            exit 1
+          else
+            echo "All good, no migrator comments were added."
+          fi