[cssom-view] Define additional feature names

[annevk]

https://drafts.csswg.org/cssom-view/#the-features-argument-to-the-open()-method

See the thread at whatwg/html#2464.

Note also the conversation at whatwg/html#1902 (comment) though. In particular, it seems that passing features at all (even if invalid) ought to trigger a different code path from passing no features. I don't see that reflected in the current algorithm.

Furthermore, given that some of these features impact the BarProp attributes, it seems these should either move to CSSOM View as well or perhaps we should define all in HTML?