Suggestion: Consider switching to "browserslist-rs"

[g-plane]

There's already browserslist-rs, so we can consider switching to it.

Pros:

• It's written in Rust and "parcel-css" is also written in Rust, so integration can be easier.
• It doesn't rely on JavaScript, so if someone uses "parcel-css" as a Rust crate, he/she can also use "browserslist" feature. Also, online demo can also support this.

Cons:

• So far, "browserslist-rs" has implemented most of the features in JavaScript-based "browserslist", but not 100%, so some rarely used features can't be available.
• "Can I Use" data are bundled, while in JavaScript-based "browserslist" those data are installed as dependencies, so data statistics may not up-to-date.

[mischnic]

https://twitter.com/devongovett/status/1481369222047481858:

There's an API to convert browserslist results into the target object expected by Parcel CSS. It's separate for performance reasons: you do this once, and then process all your files, rather than running browserslist each time.
https://github.com/parcel-bundler/parcel-css#from-javascript

[devongovett]

Added in 7d9cec0