[multiline] Add preferSingleLine option

[tommy-mitchell]

Ideally, the multiline rule should only split groups if the original string would exceed the given printWidth / classesPerLines options (etc):

// ❌ BAD: multiple groups, longer than 80 characters
<div class="text-black underline focus:font-bold focus:text-opacity-70 hover:font-bold hover:text-opacity-70" />

// ✅ GOOD: multiple groups, but shorter than 80 characters
<div class="text-black underline focus:font-bold focus:text-opacity-70" />

// ✅ GOOD: multiple groups, longer than 80 characters, wrapped to multiple lines
<div class={`
  text-black underline

  focus:font-bold focus:text-opacity-70

  hover:font-bold hover:text-opacity-70
`} />;

[schoero]

This is now implemented in version 1.7.0. Thank you for the suggestion. 🙌