Instantiates a new Latin1Codec.
If allowInvalid is true, the decode method and the converter
returned by decoder will default to allowing invalid values. Invalid
values are decoded into the Unicode Replacement character (U+FFFD).
Calls to the decode method can override this default.
Encoders will not accept invalid (non Latin-1) characters.
Source
const Latin1Codec({bool allowInvalid: false}) : _allowInvalid = allowInvalid;