Sort arbitrary properties alphabetically across multiple class lists

[thecrypticace]

Fixes tailwindlabs/prettier-plugin-tailwindcss#246

In Tailwind we sort classes alphabetically before processing to produce a deterministic order. And, when we encounter an arbitrary property we register it at that time so that's the order it'll take when sorting. In most cases this is fine because we sort up front, however, in the Prettier plugin we don't know all classes up front — each individual class list is sorted separately but uses the same internal context for performance reasons. This means that we need to do some extra bookkeeping to ensure they're sorted consistently regardless of the order of individual class lists or files scanned.

This PR does this bookkeeping and will sort classes to ensure that the arbitrary properties are always alphabetical when handled by the prettier plugin even scross separate class lists or files.

Now given these two files, a.jsx and b.jsx:

// a.jsx
export default function ComponentA() {
  return <div className="[--fg:#fff]" />
}

// b.jsx
export default function ComponentB() {
  return <div className="[--bg:#111] [--bg_hover:#000] [--fg:#fff]" />
}

If you format each individual one with prettier or format all of them at one time the order of the properties will no longer flip-flop between these two lists:

[--bg:#111] [--bg_hover:#000] [--fg:#fff]

[--fg:#fff] [--bg:#111] [--bg_hover:#000]

[RobinMalfait]

Do you think we have to worry about this in v4? I think we handle this scenario already the way we built it. 🤔

[thecrypticace]

I think we may but it entirely depends on how the APIs end up working with tools like the prettier plugin. As for right now it is already handled.