Stdin.readLineSync performance is very bad for large lines

[mraleph]

It reads input bytes one by one from the input and puts them into a growable list of <int>[].

This might lead to some very poor performance (compared to other languages) when reading exceedingly long lines from stdin.

[aam]

I guess the reason for this is that we don't want to read more bytes from the stream beyond end of the line which we ourselves identify as some form of a CR, LF sequence https://github.com/dart-lang/sdk/blob/master/sdk/lib/io/stdio.dart#L73 and below