Keyword properties added to libcss

These properties are parsed and then dropped: the cascade stores nothing, so none of them render and getComputedStyle has nothing to report for them. That is by design -- storing them would grow every element's computed style for values no layout reads. The last column records that absence rather than hiding it, so it is not counted as a failure.

What is checked: the parser knows each property, accepts its keywords, rejects a keyword it should not accept (a blanket "yes" would score the same on browserscore and be worthless), answers the same through @supports in real stylesheet text as through CSS.supports, and round-trips a value through CSSOM.