One weird JSON.parse() trick

[arindam1993]

This implements
https://www.youtube.com/watch?v=ff4fgQxPaO0
for the style spec json only. This doesn't implement it for other json objects because with those we would still like to have treeshaking.

The theory is that a static JSON.parse(large_json_string) is much faster than having a large_json_object,this is because a large_json_object is parsed by the full JavaScript parser since it can't know ahead of time if an object is pure-json.
With this change the JS parser skips that entire section since all it sees is a single string. The dedicated json parser underneath JSON.parse can then handle it much faster.
Benchmap is showing a negligible but detectible improvement in workerEvaluateScript which is exactly where we expect to see an improvement.

[mourner]

As far as I remember, I didn't pursue this idea earlier because having spec's top-level properties exposed as named exports allowed for better minifying of spec references across the codebase, as you can see by the noticeable non-compressed size increase, but it seems that gzip offsets that and the 50-byte increase is negligible, so we can proceed.