Our parsing code was treating `foo` and `foo: bar` as `<media-feature>`s
when really they need to be `(foo)` and `(foo: bar)` respectively. This
previously worked for the valid case because boolean expressions can
also have arbitrary `()` blocks. However, it meant we'd also allow them
without the parentheses which isn't valid.
So instead, parse and serialize the parentheses as part of the
`<media-feature>`. This gets us some WPT passes and fixes an Acid3
failure.
Instead of rejecting invalid media-feature values at parse time, we are
expected to parse them, and then treat them as Unknown when evaluating
their media query. To implement this, we first try to parse a valid
value as before. If that fails, or we have any trailing tokens that
could be part of a value, we then scoop up all the possible
ComponentValues and treat that as an "unknown"-type MediaFeatureValue.
This gets us 66 WPT passes.
