Add CloseDialog to IDialogService or Extension Method

[ramtechjoe]

Summary

When using the IDialogService for popups sometimes one might want to be able to close the View from the ViewModel that made the ShowDialog call. In the old NavigationService based Popup framework you could call GoBackAsync to achieve this behavior. This does not exist in the IDialogService.

API Changes

An extension method could potentially be added to IDialogService with a close method.

Intended Use Case

In our existing Xamarin Forms app we have several long running processes. To improve the user experience we have a Popup that displays a busy indicator and a message describing the on-going operation. This was easy to implement in Popups using NavigationService and calling GoBack when the job completed.