C#: improve WitException.Value type

[pavelsavara]

The pattern where the user code needs to correctly guess type of the ex.Value is fragile.

            catch (WitException e)
            {
                var error = HeaderErrorToString((HeaderError)e.Value);
                throw new HttpRequestException($"Header validation error: {error}");
            }

The cast here could throw invalid cast exception or could give misleading information.

Should we generate WitHeaderException and make the conversion on behalf of the user ?

cc @jsturtevant @dicej

[kaivol]

Alternatively, I would like to suggest not using exceptions for WIT results and instead directly returning the Result<Ok, Err>.
Using features like [MemberNotNullWhen] this could also be very ergonomic in my opinion.
It would also prevent users from accidentally throwing errors that the current function can't actually return.

[dicej]

Alternatively, I would like to suggest not using exceptions for WIT results and instead directly returning the Result<Ok, Err>. Using features like [MemberNotNullWhen] this could also be very ergonomic in my opinion. It would also prevent users from accidentally throwing errors that the current function can't actually return.

That's how it used to work prior to #968. I think both approaches have merit, and I'd suggest providing an option to allow the user to choose at binding generation time, with some reasonable default if not otherwise specified.