This change separates model binding into IModelBinderProvider (decides
which binder to use) and IModelBinder (does binding). The
IModelBinderFactory is a new services with coordinates the creation of
model binders.
- standardize on the `Type` extension method; less verbiage
- `ModelMetadata` had a redundant `IsAssignableFrom()` call
- `ModelBindingHelper.ValidateBindingContext()` over-engineered and used just once
- do useful bit inline in `KeyValuePairModelBinder` but now a silent "does not apply" case
Ryan Nowak
Doug Bunting
Ajay Bhargav Baaskaran
Derek Gray
N. Taylor Mullen