Adds info and release notes for disabledFeatures.

[rachelandrew]

Part of #7745

• adds release notes.
• adds an example to CustomElementRegistry.define.
• adds a line to the attachShadow exceptions.

[github-actions]

Preview URLs

• https://pr8228.content.dev.mdn.mozit.cloud/en-US/docs/Mozilla/Firefox/Releases/92
• https://pr8228.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/Element/attachShadow
• https://pr8228.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/CustomElementRegistry/define

Flaws

None! 🎉

External URLs

URL: /en-US/docs/Mozilla/Firefox/Releases/92
Title: Firefox 92 for developers
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/Element/attachShadow
Title: Element.attachShadow()
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/CustomElementRegistry/define
Title: CustomElementRegistry.define()
on GitHub

No new external URLs

[Rumyra]

Brill 👍