Pattern safelisting

[RobinMalfait]

Currently in the new JIT mode, we can't really use a RegExp for safelisting, because we don't have anything to match against. In AOT mode we generated everything, then when we apply the purge step, we could remove everything except of safelisted values.

This PR provides a way to apply safelisting using RegExp as well, but with a slightly different syntax:

  let config = {
    content: [{ raw: html`<div class="uppercase"></div>` }],
    safelist: [
      {
        pattern: /bg-(red)-(100|200)/,
        variants: ['hover', 'focus'],
      },
    ],
  }

Sadly we can't generate all possible combinations and then test each option against the RegExp... why not? Well...
We have 100 variants (which you can combine) and we have about 6575 utilities by default.
Instead, we generate the 6575 base utilities. These don't have any variants, e.g.: text-gray-200.
We then test the RegExp against these values. If they match, we generate the combinations using the variants you provide in the list.