feat: add resultHook (options.resultHook)

[kossnocorp]

When resultHook is passed with the query, css-loader will call it with the loader context and the result. It will allow extending css-loader functionality without using a fork. For instance, it will be possible to generate TypeScript typing files on the fly.

What kind of change does this PR introduce?
This PR introduces a feature.

Did you add tests for your changes?
Yes.

If relevant, did you update the README?
Yes.

Summary
I want to add TypeScript support to decss. To do so I have to generate type definition files. I can't do it via additional loader as I need an access to raw exports object.

Does this PR introduce a breaking change?
Nope.

Other information
¯\(ツ)/¯

[jsf-clabot]

All committers have signed the CLA.

[michael-ciniawsky]

Sry, but I have to decline this, it's out-of-scope for this loader to support specific use cases or libraries

[kossnocorp]

Well, it's sad to hear. Any alternatives to achieve that?

[alexander-akait]

Why don't parse output here https://github.com/webpack-contrib/css-loader/blob/master/lib/loader.js#L135 ?

[kossnocorp]

@evilebottnawi are you suggest to eval css-loader's output? I can see how this could help but I'm afraid there are will be too many corner cases to make it stable.

[alexander-akait]

@kossnocorp look here in theory we can use meta to pass result. But in future we remove css-modules from loader in favor postcss-plugin or css-modules-loader. You can help us with this 👍

[kossnocorp]

@evilebottnawi having meta would be great. If I properly understand webpack allows to pass additional data along with source? I'm not familiar with this feature, can you please direct me to the docs or examples of usage?

Also, @michael-ciniawsky WDYT?

[alexander-akait]

@kossnocorp no docs 😄 Yep, for pass own data from loader to other loader

[kossnocorp]

@michael-ciniawsky what do you think, won't it be out of scope?

[kossnocorp]

😬