[css-shapes-2] Add the "rotate" keyword to shape()

[noamr]

Avoids an ambiguity where the second radius and angle can both come from calc

Closes #6925

[noamr]

@tabatkins ?

[tabatkins]

I'm not against this in principle (it probably does make things slightly more readable, actually), but what's the ambiguity concern? You can statically determine the type of a calc(); it'll only be a valid radius if the type is {length:1} or {percentage:1}, and a valid angle if the type is {angle:1}.

[noamr]

I'm not against this in principle (it probably does make things slightly more readable, actually), but what's the ambiguity concern? You can statically determine the type of a calc(); it'll only be a valid radius if the type is {length:1} or {percentage:1}, and a valid angle if the type is {angle:1}.

I didn't know that! But in any case it's ambiguous for reading, especially with custom properties

[tabatkins]

Yeah that's very fair. And the whole point of this syntax is optimizing for authorability and readability, so yeah, let's go for it.