Add missing sections to fullscreen events

[queengooborg]

This PR is a follow-up to #12926. This PR adds the missing "Syntax" and "Event type" sections. The description section is omitted as I feel there is sufficient explanation in the rest of the page content already.

[github-actions]

Preview URLs

• https://pr13016.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/Document/fullscreenchange_event
• https://pr13016.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/Document/fullscreenerror_event
• https://pr13016.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/Element/fullscreenchange_event
• https://pr13016.content.dev.mdn.mozit.cloud/en-US/docs/Web/API/Element/fullscreenerror_event

Flaws

None! 🎉

External URLs

URL: /en-US/docs/Web/API/Element/fullscreenchange_event
Title: Element: fullscreenchange event
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/Element/fullscreenerror_event
Title: Element: fullscreenerror event
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/Document/fullscreenchange_event
Title: Document: fullscreenchange event
on GitHub

No new external URLs

---

URL: /en-US/docs/Web/API/Document/fullscreenerror_event
Title: Document: fullscreenerror event
on GitHub

No new external URLs

[Elchi3]

Nice! Thanks for the follow-up! 👍