1) Migrate from webpack 4 to webpack 5. This had a lot of breaking changes,
so updated multiple webpack plugins and changed the config accordingly.
2) Replaced iconfont-webpack-plugin with a more maintained webfonts-loader.
3) Replaced deprecated babel-eslint with @babel/eslint-parser.
4) Replaced optimize-css-assets-webpack-plugin with a more maintained css-minimizer-webpack-plugin.
5) Updated all other JS packages and made the required code changes.
Fixes#6207
