Implements IRegisteredTaskCollection get_Count and get_Item along with a test for both. When making the tests individually they were very similar so I merged them into one test function as per feedback.
-- v4: taskschd/regtask: Implements IRegisteredTaskCollection get_Count(). taskschd/regtask: Implements IRegisteredTaskCollection get_Item(). taskschd/tests: Adds a test for IRegisteredTaskCollection get_Item and get_Count.