[css-borders-4] Remove `/` in `corner-*-shape` grammars

[cdoublev]

The grammar of corner-*-shape shorthands requires using / to separate horizontal/vertical radii.

Name: corner-shape
Value: <corner-shape-value>{1,2} [ / <corner-shape-value>{1,2} ]?

Name: corner-top-shape, ...
Value: <corner-shape-value> [ / <corner-shape-value> ]

The corner-*-shape shorthands set the two corner-*-*-shape longhand properties of the related side. If values are given before and after the slash, then the values before the slash set the horizontal radius and the values after the slash set the vertical radius.

(nit: the second <corner-shape-value> in corner-<side>-shape should probably be optional).

But there is no horizontal/vertical definition of a corner shape like with border-radius. Is it an oversight? If so, I guess they should follow the same rules than margin, padding, right?

(edit, clarification) The canonical order of corner-shape longhands would be corner-top-left-shape, corner-top-right-shape, corner-bottom-right-shape, corner-bottom-left-shape.

[noamr]

You're right, it's an oversight. #11651