Feature Request: Support for browserslist file

[npars]

Some rules support passing a browserslist string as an argument. Other browserslist utilities (autoprefixer) support a browserslist file in the current or parent directories. It would be useful for styelint to support this file as well so that the browserslist configuration does not need to be duplicated in many places.

This applies to:
no-browser-hacks, no-unsupported-browser-features

[jeddy3]

@npars Thank you for the suggestion. As with #2054 (comment), I think your issue could be the catalyst for discussing whether these rules belong outside of core as plugins (perhaps within the same pack as they are both focused on checking things specific to the browsers being targetted). As with #2054, I think doing so would be a good thing. For example, it could facilitate experimentation with such a browserlist feature.

@stylelint/core I think we've a better understanding of the division of core rules and plugins now than we had 6 months ago. And I think 8.0.0 is shaping up as our opportunity to further stabilise core, ensuring that all the rules within it adhere to our criteria. What do you think?

As a reminder, both these rules (along with no-indistinguishable-colors, which seems mostly applicable to compiled CSS) are wrappers around 3rd party PostCSS plugins.

[jeddy3]

Closing in favour of #2079