What?

Contributes to #22890

Convert publish-related components from class components to function components.

Why?

This PR contributes to the ongoing effort to modernize the Gutenberg codebase by converting React class components to function components with hooks, as tracked in #22890.

These components are part of the core publishing flow, and modernizing them aligns with React best practices.

How?

• Replace class extends Component with function components
• Replace this.state with useState hook
• Replace lifecycle methods (componentDidMount, componentDidUpdate, componentWillUnmount) with useEffect hooks
• Replace createRef with useRef hook
• Update this.props references to use props parameter

Files changed:

• packages/editor/src/components/post-publish-button/index.js
• packages/editor/src/components/post-publish-panel/index.js
• packages/editor/src/hooks/media-upload.js

Testing Instructions

1. Run the editor publish tests:

   npm run test:unit -- --testPathPattern="packages/editor/src/components/post-publish"
   

2. Start the development environment:

   npm run dev
   

3. Create a new post with some content
4. Click the Publish button in the top bar
5. Verify the publish panel opens correctly
6. Complete the publish flow
7. Verify the post is published successfully
8. Edit the published post and verify the Update button works

Testing Instructions for Keyboard

1. Create a new post
2. Tab to the Publish button
3. Press Enter to open the publish panel
4. Tab through the publish panel options
5. Press Enter on the Publish button to publish
6. Verify focus management after publishing

Screenshots or screencast

N/A - No visual changes, only internal refactoring.