[css-borders] Can `border-*` shorthands allow independent borders?

[chharvey]

https://drafts.csswg.org/css-backgrounds-3/#the-border-shorthands

Building off of #1279 , I'd still like to suggest extending the border-* shorthand syntaxes to allow independent borders.

border-block  : <border-line> [ / <border-line> ]?
border-inline : <border-line> [ / <border-line> ]?
border        : logical? && [ <border-line> [ / <border-line> ]{0,3} ]

<border-line> = <line-width> || <line-style> || <color>

where logical is the keyword switch for logical properties, and

• <line-width>
• <line-style>
• <color>

For any given 1–2 <border-line> values (including width || style || color), the border-block shorthand would set border-block-start and border-block-end, in that order. The second value, if absent, would copy from the first value. border-inline would behave respectively for inline-side borders.

The 1–4 <border-line> values on border would indicate standard order.

In all cases, the <border-line> groups would need to be separated by slashes.