Add api-changes.yml workflow to replace danger-pr (#55341)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55341

Changelog:
[INTERNAL] [CHANGED] - Add api-changes.yml workflow to replace danger-pr for detecting changes in the js api

  The workflow:
  - Triggers on `pull_request_target` for opened, edited, reopened, and synchronize events
  - Checks out the main branch (for security, using trusted code)
  - Runs the `diff-js-api-changes` action to detect API changes
  - Posts a PR comment using the generic `post-pr-comment` action

  The PR comment script creates, updates, or deletes a bot comment based on whether
  there are any sections to report, using a marker to identify existing bot comments.

Reviewed By: huntie

Differential Revision: D90991845

fbshipit-source-id: 753475a7c24df8bc581b2ab47bfad1f5551c823c

.github/actions/diff-js-api-changes/action.yml

@@ -1,5 +1,9 @@
 name: diff-js-api-changes
 description: Check for breaking changes in the public React Native JS API
+outputs:
+  message:
+    description: Formatted markdown message describing API changes, or empty if no changes
+    value: ${{ steps.format_output.outputs.message }}
 runs:
   using: composite
   steps:
@@ -35,3 +39,35 @@ runs:
           $SCRATCH_DIR/ReactNativeApi-before.d.ts \
           $SCRATCH_DIR/ReactNativeApi-after.d.ts \
           > $SCRATCH_DIR/output.json
+
+    - name: Format output message
+      id: format_output
+      shell: bash
+      env:
+        SCRATCH_DIR: ${{ runner.temp }}/diff-js-api-changes
+      run: |
+        if [ ! -f "$SCRATCH_DIR/output.json" ]; then
+          echo "message=" >> $GITHUB_OUTPUT
+          exit 0
+        fi
+
+        RESULT=$(cat $SCRATCH_DIR/output.json | jq -r '.result // empty')
+        if [ -z "$RESULT" ] || [ "$RESULT" = "NON_BREAKING" ]; then
+          echo "message=" >> $GITHUB_OUTPUT
+          exit 0
+        fi
+
+        # Use delimiter for multiline output
+        {
+          echo "message<<EOF"
+          echo "> [!WARNING]"
+          echo "> **JavaScript API change detected**"
+          echo ">"
+          echo "> This PR commits an update to \`ReactNativeApi.d.ts\`, indicating a change to React Native's public JavaScript API."
+          echo ">"
+          echo "> - Please include a **clear changelog message**."
+          echo "> - This change will be subject to additional review."
+          echo ">"
+          echo "> This change was flagged as: \`${RESULT}\`"
+          echo "EOF"
+        } >> $GITHUB_OUTPUT

.github/actions/post-pr-comment/action.yml

@@ -0,0 +1,55 @@
+name: post-pr-comment
+description: Post or update a PR comment, or delete if no sections
+inputs:
+  sections:
+    description: 'JSON array of markdown sections to include in comment'
+    required: false
+    default: '[]'
+  header:
+    description: 'Optional header text to display at the top of the comment'
+    required: false
+    default: ''
+  marker:
+    description: 'HTML comment marker to identify this comment'
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Create, update, or delete comment
+      uses: actions/github-script@v8
+      env:
+        SECTIONS_INPUT: ${{ inputs.sections }}
+        MARKER_INPUT: ${{ inputs.marker }}
+        HEADER_INPUT: ${{ inputs.header }}
+      with:
+        script: |
+          const marker = process.env.MARKER_INPUT;
+          const header = process.env.HEADER_INPUT;
+          const sections = JSON.parse(process.env.SECTIONS_INPUT)
+            .filter(Boolean)
+            .filter(s => s.trim());
+
+          const {owner, repo} = context.repo;
+          const issue_number = context.issue.number;
+
+          const {data: comments} = await github.rest.issues.listComments({
+            owner, repo, issue_number,
+          });
+
+          const existing = comments.find(c => c.body?.includes(marker));
+
+          if (!sections.length) {
+            if (existing) {
+              await github.rest.issues.deleteComment({owner, repo, comment_id: existing.id});
+            }
+            return;
+          }
+
+          const content = sections.join('\n\n');
+          const body = header ? `${marker}\n## ${header}\n\n${content}` : `${marker}\n${content}`;
+
+          if (existing) {
+            await github.rest.issues.updateComment({owner, repo, comment_id: existing.id, body});
+          } else {
+            await github.rest.issues.createComment({owner, repo, issue_number, body});
+          }

.github/workflows/api-changes.yml

@@ -0,0 +1,28 @@
+name: Validate API snapshot changes
+
+on:
+  pull_request_target:
+    types: [opened, edited, reopened, synchronize]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  api-changes:
+    runs-on: ubuntu-latest
+    if: github.repository == 'facebook/react-native'
+    steps:
+      - name: Check out main branch
+        uses: actions/checkout@v6
+      - name: Setup Node.js
+        uses: ./.github/actions/setup-node
+      - name: Run yarn install
+        uses: ./.github/actions/yarn-install
+      - name: Run diff-js-api-changes
+        id: diff-js-api-changes
+        uses: ./.github/actions/diff-js-api-changes
+      - name: Post PR comment
+        uses: ./.github/actions/post-pr-comment
+        with:
+          marker: '<!-- api-changes -->'
+          sections: '[${{ toJSON(steps.diff-js-api-changes.outputs.message) }}]'