[css-borders-4] Specify how `corner-shape` affects `outline`

[chromium-helper]

CSSWG added the following resolution(s):

• RESOLVED: Add corner-shape to the border-radius clause in outline definition

in w3c/csswg-drafts#12194 (comment)

[chromium-helper]

I have filed issues.chromium.org/420926198

That is all that can be done here, closing issue.