Make CsvDataReader.GetFieldSpan public.

[anhaehne]

It would be great to be able to call CsvDataReader.GetFieldSpan directly to access the ReadOnlySpan<char>. My current usecase is to create hash for a single column and this way i could convert the ReadOnlySpan<char> to a ReadOnlySpan<byte> and pass that to my hash function.

Another use case would be to manually parse custom types.

[MarkPflug]

Sounds reasonable. I've quite nearly made it public in the past. The decision becomes whether to take a dependency on system.memory for netstandard2.0, or just not expose that API in ns2.0.

[anhaehne]

Since GetRawRecordSpan is also just available for .ns2.1 and up i think the easiest would be to just make it public there.

[MarkPflug]

Pushed 1.1.13 to nuget which includes this change.