Support new SASS processors

[matteeyah]

Summary

The gem currently only supports current-gem SASS processors - dartsass-sprockets and sassc-rails. The PR adds support for dartsass-rails and cssbundling-rails.

Closes #247

[matteeyah]

I hate the way these rescues nest, but I can't think of a better way for chaining requires like this.

[Peredery]

#272 suggestion

[manuelmeurer]

I don't think checking for these gems in the engine is necessary/appropriate at all.
For example, it should also work with dartsass-sprockets - another gem we would need to check for. And there might be more in the future.

Instead, I'd propose to remove these checks completely and let the user decide how to do their bundling. 🤷

[matteeyah]

@manuelmeurer I agree. Although I didn't want to make major changes to avoid a potentially lengthy discussion - my priority was to unblock using this gem with the new SASS processors. We can follow up discussing removing the requires altogether after this is merged.

[manuelmeurer]

Ok, let's wait for a maintainer to chime in! 😄
I'm happy to create a PR from my fork if removing the requires is acceptable.

[glebm]

Removing the requires would be good but we'd need to make sure it doesn't break backwards compatibility too badly.

[manuelmeurer]

I don't think backwards compatibility would be an issue here, since all these requires do is, well, requiring the gems. 😄
But maybe a minor version bump would be in order.
Let me know if you want me to create a PR for this.

[glebm]

@manuelmeurer Yes please. Let's also have a few people test the PR.

One thing that might go wrong is the require order -- I don't know if any of these preprocessors must be required before bootstrap.

[Peredery]

@glebm @manuelmeurer Hi, there seems to be something else that needs to be fixed. Please look at this ticket: #277

[Peredery]

@glebm @manuelmeurer Hi, there seems to be something else that needs to be fixed. Please look at this ticket: #277

I didn't notice it at first, because macos has by default: JavaScriptCore and it is used, but docker doesn't have it and the error is immediately noticeable there

[januszm]

I'll backport this to branch 4.6-stable unless someone is already working on it