Investigate ServerStyleSheet construction performance

It seems like new ServerStyleSheet() is our biggest SSR perf bottleneck according to the SSR benchmarks added in #2119, which in turn makes it seem like StyleSheet.clone() is the actual bottleneck.

Since as of v4 everything is in the component-context, I’m not 100% certain why we need to clone anything anymore on the server. It seems as though creating a cache of styles per each request should be a cheap operation since nothing should be shared anymore between requests?

Going to defer to @kitten’s expertise since he wrote most of that—can we maybe speed up or get rid of the cloning entirely?

[mxstbr]

@kitten that makes a lot of sense, thanks for the detailed write-up! Excited to see where this goes.

[probablyup]

Closed thanks to v5!