plus method
Returns a parser that accepts the receiver one or more times. The resulting parser returns a list of the parse results of the receiver.
This is a greedy and blind implementation that tries to consume as much input as possible and that does not consider what comes afterwards.
For example, the parser letter().plus() accepts any sequence of
letters and returns a list of the parsed letters.
Implementation
@useResult
Parser<List<R>> plus() => repeat(1, unbounded);