relnote(120): nightly disables CSS -moz-prefixed transform properties, enables CSS zoom property

[bsmth]

This PR adds a relnote about disabling -moz-transform on nightly and enabling CSS zoom.

• layout.css.zoom.enabled is true on Nightly (https://hg.mozilla.org/integration/autoland/file/tip/modules/libpref/init/StaticPrefList.yaml#l8791)
• layout.css.prefixes.transforms disabled on Nightly for now (https://hg.mozilla.org/integration/autoland/file/tip/modules/libpref/init/StaticPrefList.yaml#l8623)

Related issues and pull requests:

• Parent issue [CSS][Nightly only] Disable -moz-transform* and -moz-transition* properties #29785
• BCD (CSS zoom) relnote(120): Fx nightly enables CSS zoom property by default browser-compat-data#21122

Bugzilla:

• https://bugzilla.mozilla.org/show_bug.cgi?id=1855763
• https://bugzilla.mozilla.org/show_bug.cgi?id=390936

[github-actions]

Preview URLs

• /en-US/docs/Mozilla/Firefox/Experimental_features
• /en-US/docs/Mozilla/Firefox/Releases/120

External URLs (3)

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

• https://bugzil.la/1855763 (1 time) (Note! This may be a new URL 👀)
• https://bugzil.la/390936 (1 time) (Note! This may be a new URL 👀)

---

URL: /en-US/docs/Mozilla/Firefox/Releases/120
Title: Firefox 120 for developers

• https://bugzil.la/1855763 (1 time) (Note! This may be a new URL 👀)

[dipikabh]

LGTM. Thanks, @bsmth 👍