feat: sharedDuringBuild unocss plugin

[hi-ogawa]

Experimenting with Plugin.create and sharedDuringBuild introduced in vitejs/vite#16471 (comment)

summary

• Token extraction is done for all environments using transform hook
• virtual:unocss.css is imported by single environment ("client" in my case)
  • During dev, this will set up HMR via environment.hot
  • During build, this will set up "delayed" css transform based on renderChunk + vite:css-post trick.
    Since the build order is react-server -> client, at the time of client renderChunk, it has collected all tokens from both environments.

todo

• dev, hmr, fouc
• build
• test
• feedback
  • create is awesome
    • since create(environment) already gives environment.moduleGraph, hot, etc... during dev, configureServer(server) was not necessary.