Consolidate registration to single configuration object and optimize registration

[jbogard]

Consolidates registration and scanning into a single configuration object; Only registers extra behaviors (pre/post processor, etc.) if there are any available.

API changes

All configuration would be consolidated into a single method (instead of parameters in an overload):

public static class ServiceCollectionExtensions {
-    public static IServiceCollection AddMediatR(this IServiceCollection services, params Assembly[] assemblies)
-    public static IServiceCollection AddMediatR(this IServiceCollection services, Action<MediatRServiceConfiguration>? configuration, params Assembly[] assemblies)
-    public static IServiceCollection AddMediatR(this IServiceCollection services, IEnumerable<Assembly> assemblies, Action<MediatRServiceConfiguration>? configuration)
-    public static IServiceCollection AddMediatR(this IServiceCollection services, params Type[] handlerAssemblyMarkerTypes)
-    public static IServiceCollection AddMediatR(this IServiceCollection services, Action<MediatRServiceConfiguration>? configuration, params Type[] handlerAssemblyMarkerTypes)
-    public static IServiceCollection AddMediatR(this IServiceCollection services, IEnumerable<Type> handlerAssemblyMarkerTypes, Action<MediatRServiceConfiguration>? configuration)
+    public static IServiceCollection AddMediatR(this IServiceCollection services, Action<MediatRServiceConfiguration> configuration)
}

All the parameters are now moved to the MediatRServiceConfiguration object, including a pass-through method to add behaviors:

public class MediatRServiceConfiguration {
-    public Func<Type, bool> TypeEvaluator { get; private set; } = t => true;
-    public Type MediatorImplementationType { get; private set; }
-    public ServiceLifetime Lifetime { get; private set; }
+    public Func<Type, bool> TypeEvaluator { get; set; } = t => true;
+    public Type MediatorImplementationType { get; set; } = typeof(Mediator);
+    public ServiceLifetime Lifetime { get; set; } = ServiceLifetime.Transient;
+    public RequestExceptionActionProcessorStrategy RequestExceptionActionProcessorStrategy { get; set; } = RequestExceptionActionProcessorStrategy.ApplyForUnhandledExceptions;
+    internal List<Assembly> AssembliesToRegister { get; } = new();
+    public List<ServiceDescriptor> BehaviorsToRegister { get; } = new();

// These methods removed to instead use the properties directly
-    public MediatRServiceConfiguration Using<TMediator>() where TMediator : IMediator
-    public MediatRServiceConfiguration AsSingleton()
-    public MediatRServiceConfiguration AsScoped()
-    public MediatRServiceConfiguration AsTransient()
-    public MediatRServiceConfiguration WithEvaluator(Func<Type, bool> evaluator)

// These replace the overloads for passing in types or assemblies to scan
+    public MediatRServiceConfiguration RegisterServicesFromAssemblyContaining<T>()
+    public MediatRServiceConfiguration RegisterServicesFromAssemblyContaining(Type type)
+    public MediatRServiceConfiguration RegisterServicesFromAssembly(Assembly assembly)
+    public MediatRServiceConfiguration RegisterServicesFromAssemblies(params Assembly[] assemblies)

// These are new methods to add concrete behaviors but merely passthrough the configuration to the underlying `IServiceCollection`
+    public MediatRServiceConfiguration AddBehavior<TServiceType, TImplementationType>(ServiceLifetime serviceLifetime = ServiceLifetime.Transient)
+    public MediatRServiceConfiguration AddBehavior(Type serviceType, Type implementationType, ServiceLifetime serviceLifetime = ServiceLifetime.Transient)
// This method is for registering an open behavior still passing through the configuration
+    public MediatRServiceConfiguration AddOpenBehavior(Type openBehaviorType, ServiceLifetime serviceLifetime = ServiceLifetime.Transient)

Behavior changes

The service scanning was modified to only register with the container the "built-in" behaviors of:

• RequestPreProcessorBehavior<,>
• RequestPostProcessorBehavior<,>
• RequestExceptionProcessorBehavior<,>
• RequestExceptionActionProcessorBehavior<,>
  When "Sub-behaviors" of those types are found in the IServiceCollection.

There are performance implications to resolving those sub-behaviors, so if they don't exist, the built-in behavior won't be registered.

[jbogard]

Fixes #829