Allow BehaviorsAttribute inheritance

[swimmesberger]

By inheriting from the BehaviorsAttribute (it's currently sealed) we could combine multiple behaviors in e.g. a common behavior type for certain projects:

public sealed class DefaultBehaviorsAttribute: BehaviorsAttribute {
    public DefaultBehaviorsAttribute() : base(typeof(ValidationBehaviour<,>), typeof(TransactionBehavior<,>)) { }
}

// usage
[Handler]
[DefaultBehaviors]
internal static partial class AddDataSourceCommand {}

[viceroypenguin]

I've done some review on this, and I think this may be possible, but with a very severe restriction:

• derived attribute would have to take no parameters and provide a static sequence of types to the base class constructor.

The reason for this restriction is that the behaviors list is determined at compile time, so any run-time generation of type sequences would not be possible.

I will take a look over the next few weeks and try to get an update out implementing this though!

[viceroypenguin]

@swimmesberger what would you think about the following instead:

[Behaviors(
  typeof(ValidationBehaviour<,>), typeof(TransactionBehavior<,>)
)]
public sealed class DefaultBehaviorsAttribute : Attribute;

[swimmesberger]

@viceroypenguin sorry, for the late response. Thanks for implementing this. Still using immediate.Handlers in my project 😎🎉