ensure \n\n are kept as \n\n

When splitting `'foo\n\nbar'` by `\n`, you will get `['foo', '', 'bar']`.

The `''` value will result in `[]` after the word wrapping. This
information gets lost when we `flatMap`, so let's keep the newline using
`['']` as the fallback.

packages/@tailwindcss-upgrade/src/utils/renderer.ts

@@ -44,7 +44,7 @@ export function wordWrap(text: string, width: number): string[] {
   // Handle text with newlines by maintaining the newlines, then splitting
   // each line separately.
   if (text.includes('\n')) {
-    return text.split('\n').flatMap((line) => wordWrap(line, width))
+    return text.split('\n').flatMap((line) => (line ? wordWrap(line, width) : ['']))
   }
 
   let words = text.split(' ')