Returns a parsed json map of this string.
map
Example: '{"name": "John", "age": 30}'.parseJson -> {'name': 'John', 'age': 30}.
'{"name": "John", "age": 30}'.parseJson
{'name': 'John', 'age': 30}
Map<String, dynamic>? get parseJson => jsonDecode(this) as Map<String, dynamic>?;