UTF8 Support via GetBytes or GetFieldValue

See discussion in [.Net Repo ](https://github.com/dotnet/runtime/issues/57262), specifically this [comment](https://github.com/dotnet/runtime/issues/57262#issuecomment-897485956)

### Is your feature request related to a problem? Please describe.
There is Utf8JsonWriter which allows us to write UTF8 Strings directly to the browser. If I get data from MS SQL Server which might be stored in UTF8 already, it's always converted to C# UTF16 and then back to UTF8

### Describe the solution you'd like
I'd like to be able to get the ReadOnlySpan or byte[] of the UTF8 value in order to directly use it in Utf8JsonWriter (or whatever API). It would be ok for me to just get the raw byte[] value in the encoding of the server, meaning different results for varchar, varchar collate *utf8 and nvarchar.

### Describe alternatives you've considered
Well, the alternative is to just not do it and accept the overhead produced