Add "method of opting into following the visual order", currently `focus-order` …maybe eventually

[Schweinepriester]

• https://twitter.com/bramus/status/1538622128345518080
• [css-flexbox][css-grid] Providing authors with a method of opting into following the visual order, rather than logical order w3c/csswg-drafts#7387

Way way too early to actually add it of course, but once again using this to ~publicly track it for myself because exciting 0:-)

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If you don't want these kind of issues, let me know, then I'll move out 0:-)