Add prefixedRange to CSV Schema Language 1.2

[DavidUnderdown]

Service numbers often have a non-numeric prefix, but then the numeric part may be within a well-defined numeric range. It's possible to do a bit of checking that the number is within an expected range using regex, but it's not easy to read, and difficult to be absolutely precise. It would be helpful if you could do something like prefixedRange("JX ",125000,145750).

There's some similarity between this and being able to supply a fixed path to prefix to a file expression (though the implementation would need to be different.