T/1945: Bumped style-loader to v1.0.0. Aligned configurations and documentation to the new loader API

[oleq]

Suggested merge commit message (convention)

Other: Bumped style-loader to v1.0.0. Aligned configurations and documentation to the new loader API. Closes #1945.

BREAKING CHANGE: The entire project migrated to style-loader v1.0.0 which has a different configuration syntax. Make sure your webpack configuration files are up–to–date to avoid future errors.

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Additional information

This PR requires other PRs:

• t/ckeditor5/1945: Bumped style-loader to v1.0.0. Aligned the webpack config to the new loader API. ckeditor5-build-classic#82
• t/ckeditor5/1945: Bumped style-loader to v1.0.0. Aligned the webpack config to the new loader API. ckeditor5-build-balloon#27
• t/ckeditor5/1945: Bumped style-loader to v1.0.0. Aligned the webpack config to the new loader API. ckeditor5-build-balloon-block#10
• t/ckeditor5/1945: Bumped style-loader to v1.0.0. Aligned the webpack config to the new loader API. ckeditor5-build-decoupled-document#22
• t/ckeditor5/1945: Bumped style-loader to v1.0.0. Aligned the webpack config to the new loader API. ckeditor5-build-inline#16
• t/ckeditor5/1945: Bumped style-loader to v1.0.0. Aligned the webpack config to the new loader API. ckeditor5-dev#540

[Reinmar]

I checked that there are far more dependencies that we can upgrade in builds now:

     "postcss-loader": "^3.0.0",
-    "raw-loader": "^1.0.0",
-    "style-loader": "^0.23.0",
-    "uglifyjs-webpack-plugin": "^1.2.7",
-    "webpack": "^4.15.0",
-    "webpack-cli": "^3.0.8"
+    "raw-loader": "^3.1.0",
+    "style-loader": "^1.0.0",
+    "uglifyjs-webpack-plugin": "^2.2.0",
+    "webpack": "^4.39.1",
+    "webpack-cli": "^3.3.6"
   },

I'd upgrade all at once. Also, as long as we don't force you to make them, they are not breaking. E.g. you only need to change your webpack config if you bumped style-loader in your package.json and this is your call. So, if this is the same situation with all the other pkgs, then we can safely do it even now.

So todo:

1. update other build-step deps (because there's more packages than that that we'll need to upgrade),
2. make a decision whether this is a safe change that we can do right now.

[Reinmar]

As commented.

[oleq]

I bumped other deps up.

The thing with the uglify plugin is that we cannot go to 2.0 because it's not es6 compatible. We'd have to use terser.

Switch back to uglify-js (uglify-es is abandoned, if you need uglify ES6 code please use terser-webpack-plugin).

Other than that, things look like they're working (raw–loader in particular).