Implement IServiceManager interface - #7946

/// <summary>
/// Defines a mechanism for registering and retrieving a service object; 
/// that is, an object that provides custom support to other objects.
/// </summary>
public interface IServiceManager : IServiceProvider
{
       /// <summary>
       /// Allows extension applications to register some specific service by its type.
       /// Only one service of a given type can be registered.
       /// </summary>
       /// <typeparam name="T">Type of the service</typeparam>
       /// <param name="service">The service object to register</param>
       /// <returns>A key for the registered service if registeration is 
       /// successful else null.</returns>
       string RegisterService<T>(T service);

       /// <summary>
       /// Unregisters a service of given type registered with given key. 
       /// </summary>
       /// <typeparam name="T">Type of the service</typeparam>
       /// <param name="serviceKey">The service key to ensure that only authorized
       /// client is unregistering this service type.</param>
       /// <returns></returns>
       bool UnregisterService<T>(string serviceKey);

       /// <summary>
       /// Gets the service object of the specified type.
       /// </summary>
       /// <typeparam name="T">Type of the service</typeparam>
       /// <returns>The service object if registered else null</returns>
       T Service<T>();
}