Rethink ADBC 1.1 support for C# implementation

### What feature or improvement would you like to see?

With renewed interest in revving the spec, this seems like a good time to rethink the stalled support for ADBC 1.1 in the C# implementation. Previously, I'd thought to take the opportunity to make a bunch of breaking changes and then declare a "1.0" but nearly 1.5-years later the opportunity for breaking changes is arguably past. So now the task will be to take the previously-defined "1.1" classes and merge them in with the "1.0" classes such that they gain 1.1 features but in a backwards-compatible fashion.