unescape method
Implementation
String unescape(String v) => v.replaceAllMapped(
RegExp("\\\\[nrtbf\"']"),
(v) => const {
'n': '\n',
'r': '\r',
't': '\t',
'b': '\b',
'f': '\f',
'v': '\v',
"'": "'",
'"': '"'
}[v.group(0)!.substring(1)]!);