Consider patternizing concern overrides for filters

[rynowak]

Code sample from #4506 (comment)

public interface IFooConcernFilter
{
    // Just a marker
}

public class MyGlobalFooConcernFilter : IFooConcernFilter, IActionFilter
{
    public void OnActionExecuting(...)
    {
        if (!IsClosestFooConcernFilter(context)
        {
            return;
        }
    }

    private bool IsClosestFooConcernFilter(FilterContext context)
    {
            // Determine if this instance is the 'effective' foo concern policy.
            for (var i = filters.Count - 1; i >= 0; i--)
            {
                var filter = filters[i];
                if (filter is IFooConcernFilter)
                {
                    return object.ReferenceEquals(this, filter);
                }
            }

            Debug.Fail("The current instance should be in the list of filters.");
            return false;
    }
}

public class IgnoreFooConcernAttribute : Attribute, IFooConcernFilter
{
    // Also just a marker
}

This gives [IgnoreFooConcern] overriding behavior. If you slap that on a controller or action, then the global filter knows to shut itself off.

We do this kind of thing frequently in the framework, and it's a non-obvious pattern. Maybe we should add some kind of infrastructure/extensions to make this easier for users to grok.

[rynowak]

I'd like to update this proposal to just put the code we described above as a protected method on filter context. Removing needs design, this is a trivial amount of work.

[rynowak]

c09575d