indentLines method
Prepends prefix to every line (after splitting by newline).
Line breaks are normalized to \n before splitting. prefix must not be null.
Returns a new string with each line prefixed.
Example:
'a\nb'.indentLines(' '); // ' a\n b'
Implementation
@useResult
String indentLines(String prefix) {
if (isEmpty) return this;
final List<String> lines = split('\n');
return lines.map((String line) => prefix + line).join('\n');
}