Change dark selector so @apply works correctly with pseudo elements

[thecrypticace]

When using the class strategy the dark mode selector is :is(.dark &). However, our code that handles hoisting pseudo elements outside of :is(…) doesn't handle this properly when using @apply.

Given the following code:

::-webkit-scrollbar-track {
  @apply dark:bg-black;
}

You would end up with something like this:

:is(.dark )::-webkit-scrollbar-track {
  --tw-bg-opacity: 1;
  background-color: rgb(0 0 0 / var(--tw-bg-opacity));
}

The selector above is is equivalent to .dark::-webkit-scrollbar-track which is incorrect. We want a selector that is equivalent to .dark ::-webkit-scrollbar-track.

This PR changes the selector we define for dark mode to &:is(.dark *). This is functionally equivalent to the previous selector and means we don't have to make any fixes inside @apply's selector handling. As a result you'll end up with this CSS:

:is(.dark *)::-webkit-scrollbar-track {
  --tw-bg-opacity: 1;
  background-color: rgb(0 0 0 / var(--tw-bg-opacity));
}

Which is equivalent to .dark ::-webkit-scrollbar-track and thus works as expected.

Fixes #13037

[RobinMalfait]

Such a small change, love it!