Add an abstraction for resolving an executable

[glen-84]

Product

Hot Chocolate

Is your feature request related to a problem?

An example of the problem can be found in #6833 (comment).

The solution you'd like

From Michael, something like:

public interface IExecutableResolver
{
    IExecutable<T> Resolve<T>(object source);
}

Registered in the DI container, this would allow for middleware like the SingleOrDefaultMiddleware to execute SingleOrDefaultAsync on the appropriate IExecutable<T> implementation (f.e. EfQueryableExecutable<T>).