`css-loader` is deprecated - get rid of it

[birdofpreyru]

https://webpack.js.org/guides/native-css

[birdofpreyru]

Problems:

Latest Webpack requires Jest tests in ESM mode, and switching Jest tests to ESM mode causes some errors in Babel transformations. So, it is not a quick change, it requires some troubleshooting.

[birdofpreyru]

Also, the way CSS transformation is currently hidden in the core of Webpack code (without public export of its core pieces, and with lots of dependencies on the internal Webpack stuff) makes it non-trivial to simply re-use Webpack logic by importing it.