Update compat data for requiredExtensions (#18144)
Update compat data for requiredExtensions (#18144)

* Update compat data for requiredExtensions

- Basic support (i.e. recognize XHTML namespace) was added in Firefox 1.9.1 [1], Safari 8 [2] and Chromium 81 [3].
- MathML support (i.e. recognize MathML namespace) was added in the same browser versions [1] [2] [4], although Chromium's one is still under a flag.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=449746 (Firefox 1.9.1, MathML & XHTML)
[2] https://bugs.webkit.org/show_bug.cgi?id=88188 (Safari 8, MathML & XHTML)
[3] https://chromiumdash.appspot.com/commit/c78acd517835db96c3b50f11d30eb2a77e9910c1 (Chromium 81, XHTML)
[4] https://chromiumdash.appspot.com/commit/719b33b59410a6a4623769c3a93220db03dfa51b (Chromium 81, MathML)

* Update svg/attributes/conditional_processing.json

Co-authored-by: Florian Scholz <3f4bb586f04a0c1d93eadab9363a8a3183b4860c@florianscholz.com>

Co-authored-by: Florian Scholz <3f4bb586f04a0c1d93eadab9363a8a3183b4860c@florianscholz.com>
mdn/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data