[css-logical-1] Invalid `initial` of `border-*-radius` properties

[cdoublev]

The initial field of the border-*-radius properties are defined with Same as border-top-left-radius, which cannot be parsed against the value field, which is annoying for CSS tools that use this data, eg. to set a longhand value that is missing in a shorthand declaration value.

I suggest using 0 or some kind of redirection markup that w3c/reffy can read to extract the proper value.

FYI, @tidoust.