Don't duplicate layer output when scanning content with variants + wildcards

[thecrypticace]

Tailwind CSS treats * as special internally. Because of this if it scanned content which contained something like focus:* it would then generate duplicate CSS — including base layers. The best way to fix for this would be to use a Symbol in place of the special character — however the stringy-ness of class candidates is fairly well baked into assumptions across the codebase. Instead, by using new String(…), we get an identical API surface to normal strings along with the behavior of something similar to a Symbol as identity comparisons against "*" will fail since we have a unique, non-interned object.

Fixes #7204

[thecrypticace]

@RobinMalfait Does this approach seem okay? It feels pretty sound. I'm just not sure if we want to go ahead and try to use proper Symbols instead even though it'd be a good bit more work. I'm not sure if its worth the effort at the moment — thoughts?

[RobinMalfait]

Yep the uniqueness of new String() is quite clever.
My only concern would be if you have your own custom rules that look something like:

    @tailwind base;
    @tailwind components;
    @tailwind utilities;

    * {
      color: red;
    }

    .combined,
    * {
      text-align: center;
    }

    @layer base {
      * {
        color: blue;
      }
      .combined,
      * {
        color: red;
      }
    }

But it seems like that works as expected 👍

[thecrypticace]

Ah, that's a good test to add though. I'll add that and then merge this in!