iOS Swift Conversion (#2527)

Converts iOS implementation from Objective-c to Swift

# During the conversion process some updates to the code structure were also made
- Modularize codebase from single file to smaller focused files
- Untangled large nested IF statements
- Added more null checks, since Swift is more strict with null pointers
- Added property to allow for decoding of local video sources with self contained key for offline playback
- Updates example apps to test react-native 0.63.4 and uses auto native dependency imports for android and ios

examples/basic/windows/VideoPlayer/MainPage.idl

@@ -0,0 +1,8 @@
+namespace videoplayer
+{
+    [default_interface]
+    runtimeclass MainPage : Windows.UI.Xaml.Controls.Page
+    {
+        MainPage();
+    }
+}