Add blocklist support from v3 config files

[thecrypticace]

This PR adds support for the blocklist config option when using a JS config file in v4. You can now block certain classes from being generated at all. This is useful in cases where scanning files sees things that look like classes but are actually not used. For example, in paragraphs in a markdown file:

// tailwind.config.js
export default {
  blocklist: ['bg-red-500'],
}

<!-- index.html -->
<div class="bg-red-500 text-black/75"></div>

Output:

.text-black/75 {
  color: rgba(0, 0, 0, 0.75);
}

[thecrypticace]

I'll fix the changelog conflict when we're ready to merge.

[RobinMalfait]

Nice! Can we add a test to make sure that @apply bg-white also doesn't work?

This is what v3 does: https://play.tailwindcss.com/ewH6tmV5q4?file=css

[thecrypticace]

Good call — I fixed that case and added a test for it.

[thecrypticace]

I think there's some wiggle room in the future here such that blocklist only applies to generated candidates. This is because the nature of content scanning means you're likely scanning content you can't change for the sake of Tailwind. But @apply you always write explicitly and the failure mode is always hard crash when something doesn't exist.