chore(tools): Optimize build by switching css processing to esbuild

[pskelin]

yarn start on mac improvement from 15s -> 8s

Important: note this esbuild change in @import behaviour:
https://esbuild.github.io/content-types/#css-import-order

CSS processing (resolving imports and minification) is switched from postcss to esbuild for much better performance.

• the custom postcss plugins for generating JS/TS and JSON files are switched to esbuild plugins and run on the string content only
• removal of duplicate selectors is improved by running in onExit and this is the only remaining postcss plugin running on string only, no file operations
• all other postcss plugins and build steps are removed

Other improvements

• all JSON files are generated in dist and this saves a copy step
• starting the watch mode for templates, CSS files and i18n processes all files again and if the content is the same, they are not changed. So the normal start is:
  • process all non-code files and generate a TS/JSON file
  • start vite in dev mode (this already works but doesn't refresh on changes)
  • start all watch tasks parallel to the vite start
• the watch tasks now compete with the vite page load and make it a bit slower, so this change delays the watch by 5 seconds so that vite can start faster