refactor(core): add jsdoc comments for ExtensionManager

[bdbch]

Changes Overview

I added a few missing JS Docs to the extension manager to make understanding said class a bit easier.

Implementation Approach

N/A

Testing Done

N/A

Verification Steps

N/A

Additional Notes

N/A

Checklist

• I have renamed my PR according to the naming conventions. (e.g. feat: Implement new feature or chore(deps): Update dependencies)
• My changes do not break the library.
• I have added tests where applicable.
• I have followed the project guidelines.
• I have fixed any lint issues.

[netlify]

✅ Deploy Preview for tiptap-embed ready!

Name	Link
🔨 Latest commit	49d60f8
🔍 Latest deploy log	https://app.netlify.com/sites/tiptap-embed/deploys/66423707e91d9800081d4bb7
😎 Deploy Preview	https://deploy-preview-5140--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.