Getting currently focused element is not supported

[shyunMin]

• Requirement
  Getting currently focused element to support Xamarin.UITest.IApp.EnterText method.
  (https://developer.xamarin.com/api/member/Xamarin.UITest.IApp.EnterText/p/System.String/)

• Expected behavior
  If the ContentPage has an Entry, the Entry will be returned as a currently focused element after the page is appeared.

• Related TC
  EntryUITests.Completed

• Issue
  There is a difference between expected behavior and Tizen platform behavior.
  In Tizen platform, Entry doesn't have a focus until it is clicked.