[Feature Request] Add {pseudo-classes}:related and related-{pseudo-classes}:{tailwind-class-name}

[Scrum]

This option is very similar in its ideology with group-hover and [group-focus](https://tailwindcss.com/docs/pseudo-class-variants/#group-focus- v1-3-0) but unlike these, it is designed for nextSiblings elements.

Demo

Usage example

<div class="relative pt-4 m-4">
  <input 
    type="text" 
    id="name" 
    pattern="{1,}"
    required
    class="
      border-b w-64 pb-2 
      
      focus:outline-none 
      focus:border-blue-500 
      focus:related
      
      valid:border-green-500
      valid:related
    "
  />
  <label 
    for="name" 
    class="
      absolute left-0 top-0 cursor-text 
      
      mt-4
      text-gray-500 
      
      related-valid:mt-0 
      related-valid:text-gray-700
      related-valid:text-xs
      
      related-focus:mt-0
      related-focus:text-gray-700 
      related-focus:text-xs
     "
  >You name</label>
</div>