FF152 Relnote TC39 Iterator includes proposal

[hamishwillee]

FF152 adds support for the TC39 Iterator proposal in https://bugzilla.mozilla.org/show_bug.cgi?id=2025779 behind pref javascript.options.experimental.iterator_includes

This adds a release note and an experimental features entry.
The docs are being done in a separate PR.

Related docs work can be tracked in #44158

[github-actions]

Preview URLs (2 pages)

• /en-US/docs/Mozilla/Firefox/Experimental_features
• /en-US/docs/Mozilla/Firefox/Releases/152

Flaws (2)

Found an unexpected or unresolvable flaw? Please report it here.

URL: /en-US/docs/Mozilla/Firefox/Experimental_features
Title: Experimental features in Firefox
Flaw count: 1

• broken_links:
  • Link /en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/includes doesn't resolve

---

URL: /en-US/docs/Mozilla/Firefox/Releases/152
Title: Firefox 152 release notes for developers (Beta)
Flaw count: 1

• broken_links:
  • Link /en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator/includes doesn't resolve

External URLs (2)

URL: /en-US/docs/Mozilla/Firefox/Experimental_features
Title: Experimental features in Firefox

• https://bugzil.la/2025779 (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Mozilla/Firefox/Releases/152
Title: Firefox 152 release notes for developers (Beta)

• https://bugzil.la/2025779 (1 time) (Note! This may be a new URL 👀)