Extract special @("@")md:… syntax in Razor files

[RobinMalfait]

This PR fixes an extraction issue in Razor files where @@md:bg-red-500 can't always be extracted properly. We already convert @@md:bg-red-500 to @md:bg-red-500 but in certain situations Razor will emit the double @@ to the DOM.

A workaround in Razor land would be to write @("@")md:bg-red-500 instead. See: dotnet/aspnetcore#38595 But then we don't extract the @md:bg-red-500 properly anymore.

This is where this PR comes in, essentially we will pre process the Razor contents and apply the following replacement internally:

- @("@")md:bg-red-500
+      @md:bg-red-500

Notice that the ) looks like it's replaced with @. This will have a small side effect later when we get to the testing part.

But this way we properly see the @md:bg-red-500 class during class extraction.

Warning

There is technically a bug here because of the replacement with @, because if you now run the npx @tailwindcss/upgrade@latest tool, then we would replace )md:bg-red-500 if changes are required, not the @("@")md:bg-red-500 part. We can try to fix that in this PR but it seems unlikely that we will actually run into this issue realistically speaking. I think fixing the actual extraction here is much more important than the upgrade tooling that could fail if we ever have to migrate @md:… to something else.

Fixes: #17424

Test plan

1. Added a test to verify the fix

2. Existing tests pass

3. Verified this in the extractor tool, but it looks a tiny bit funky.

   Typically we remove characters by replacing it with a space . But this time, we replace it with some spaces and an @ character that didn't exist at that specific position. If you look at the diff above, you will notice that ) was replaced with @.

   That's why in the extractor tool it is highlighted that it could extract it, but it's just funny looking because it highlights )md:bg-red-500