Pseudo-element selectors incorrectly transformed with cascade: false

[Rich-Harris]

Can't show in the REPL, because it doesn't use cascade: false (we need to add some compiler options to the UI), but this fails:

<span></span>

<style>
  span::after {
    content: 'i am a pseudo-element';
  }
</style>

The selector becomes span::after[svelte-123xyz] instead of span[svelte-123xyz]::after.