feat(placeholder): allow editor-is-empty class on any node

[bdbch]

Please describe your changes

This PR implements a new option for @tiptap/extension-placeholder that will allow users to enable more nodes than just paragraphs as empty for the editor-is-empty empty check.

How did you accomplish your changes

Instead of creating an empty doc copy, I'm directly checking the current document childCount, check if the first element is a valid node (as configured or is it not a atom or leaf) and then enable the class for valid nodes found at the first position of the editor.

How have you tested your changes

I used the local development environment for testing.

How can we verify your changes

1. Checkout this PR
2. Go to the Placeholder demo of your choice
3. Add the option considerAnyAsEmpty: true
4. Test inside your browser if the empty-editor placeholder will be shown for headlines too

Remarks

• In the future we could even make this more granular by adding node type filters

Checklist

• The changes are not breaking the editor
• Added tests where possible
• Followed the guidelines
• Fixed linting issues

Related issues

• No related issues

[netlify]

✅ Deploy Preview for tiptap-embed ready!

Name	Link
🔨 Latest commit	9f45028
🔍 Latest deploy log	https://app.netlify.com/sites/tiptap-embed/deploys/64dcfeba6c51ee0008e69a4e
😎 Deploy Preview	https://deploy-preview-4335--tiptap-embed.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.