Detect / within values of a multi-value borderRadius shorthand

[nmn]

NOTE: This is a very specific, edge-case bug.

When in styleResolution: 'legacy-expand-shorthands', we expand shorthand CSS properties into their constituent longhand properties. This includes borderRadius.

However, when splitting borderRadius, we treat a space separation to imply the next direction. This misses the edge-case that 1px / 2px is a valid value for a single corder when used in a border-radius.

e.g.

borderRadius: '1px / 2px 3px 4px 5px'

should be split into:

borderStartStartRadius: '1px / 2px',
borderStartEndRadius: '3px',
borderEndEndRadius: '4px',
borderEndStartRadius: '4px',