ugh. tried everything, but seems that async imports work the best for proper chunk splitting
- handles dependencies correctly, only options page code is remaining in options_page.js
- force naming chunks is nice cause they end up with random numeric names in optimized build
- still don't understand how it works without including codemirror.js into the html page

also tried
- static import + splitting chunks like this
     cacheGroups: {
       codemirror: {
         test: /[\\/]node_modules[\\/].*codemirror/,
         name: 'codemirror',
         chunks: 'all',
       },
     },
  this works, but doesn't split out dependencies of codemirror?
  so still end up with some crap in options_page.js

- specifying codemirror entry point and adding to dependsOn
     'codemirror': {
       // TODO no need for codemirror source map??
       import: [
         "codemirror",
         "@codemirror/view",
         "@codemirror/language",
         "@codemirror/search",
         "@codemirror/autocomplete",
         "@codemirror/state",
         "@codemirror/lang-css",
         "@codemirror/lang-javascript",
       ],
     }
   this splits out everything properly... but then options page failed loading another chunk, webext-options-sync
   no idea why, couldn't figure out

…se mode