feat(compiler): foundation css prefix

[ematipico]

Summary

This PR adds a new feature to the Rome compiler. Now that our CSS parser is gaining traction, we can start applying transformations to them during the compilation phase.

I wanted to set up the foundations of a sort of autoprefixer. I didn't call it that way for obvious reasons. So for now, I called it css-prefix but feel free to suggest a better name. Maybe it should not be called css-prefix if we think that its purpose is broader.

I created a index.ts where we could put all the CSS transformations and each transformation will be its own file.

I also fixed a small issue inside the CSS format.

Test Plan

I set up a new test fixtures which is better compared to what we had.

[jer3m01]

Just me being picky but wouldn't css-prefixer be better, following parser. Doesn't matter much and the more I think about it the less sense the difference makes.

Also I know this is just a foundation but there are a few other prefixes we could add (-moz-, don't know if we want -ms- as it's on its final version and most MS products are dropping support for it soon).
There are also value prefixes i.e. display: -webkit-box.

Personally I'd use something different than just if statements in a single code block to do all the prefixes as it would get tedious if there are a lot.
Don't have any idea on what the implementation would look like though.

And the ability to use something like browserlist could be considered (but than we would need it make a custom implementation or port it).

Anyway, looks great!

[ematipico]

@jer3m01 thank you very much for your feedback, it's really appreciated!

I initially implemented the logic of the transition by taking what autoprefixer does. Although I totally overlooked the browser part! I noticed that the playground has set the value "browser" to"last 4 versions" that's why I worked only on two prefixes.

Totally missed that one and your comment raised it, thank you. We should plan this more thoroughly I guess, as the part of the target browser should come from the configuration.

I think this prefixer should be more than just transformations, and it should be implemented more like the linter is, with some caching under hood, maybe.