This reverts 0e3487b9ab.
Back when I made that change, I thought we could make our StyleValue
classes match the typed-om definitions directly. However, they have
different requirements. Typed-om types need to be mutable and GCed,
whereas StyleValues are immutable and ideally wouldn't require a JS VM.
While I was already making such a cataclysmic change, I've moved it into
the StyleValues directory, because it *not* being there has bothered me
for a long time. 😅
The goal here is to do something a bit smarter with the parsing here
than we do for properties. Instead of the JSON saying "here are the
values, and here are the keywords, and we can have up to 3", here we
place the syntax in the JSON directly (though currently broken up as
one string per option) and then we attempt to parse each one in
sequence. It's something we'll need eventually for `@property` among
other things.
...However, in this first pass, I've gone with the simplest option of
hard-coding the types instead of figuring them out properly. So there's
a PositivePercentage type and a UnicodeRangeTokens type, instead of
properly implementing the grammar for those in a generic way.
Add a new JSON file describing at-rule descriptors, and then use it to
generate a DescriptorID enum, and code to check if it's accepted in a
given at-rule.
