add sideEffects false for tree-shaking in webpack

[mscolnick]

No description provided.

[alexdima]

I had to revert this, because it led to all the CSS imports being ignored...

[mscolnick]

ah ok, sorry about that. the change should've been this:

  "sideEffects": [
    "*.css"
  ],

still ok if i submit the PR?

[alexdima]

Sure, but can you please test the following before:

• https://github.com/Microsoft/monaco-editor-webpack-plugin
  > npm run test
  (open in a localhost server the /test/dist folder)

• https://github.com/Microsoft/monaco-editor-samples/tree/master/browser-esm-webpack
  > ./node_modules/.bin/webpack
  (open in a localhost server the /browser-esm-webpack/dist folder)

• https://github.com/Microsoft/monaco-editor-samples/tree/master/browser-esm-webpack-small
  > ./node_modules/.bin/webpack
  (open in a localhost server the /browser-esm-webpack-small/dist folder)