Handle audio interruptions on iOS/tvOS. Fixes bugs 2569 and 2960.

src/audio/coreaudio/SDL_coreaudio.h

@@ -34,6 +34,7 @@
 #include <CoreServices/CoreServices.h>
 #else
 #import <AVFoundation/AVFoundation.h>
+#import <UIKit/UIApplication.h>
 #endif
 
 #include <AudioToolbox/AudioToolbox.h>
@@ -56,6 +57,9 @@ struct SDL_PrivateAudioData
     SDL_atomic_t shutdown;
 #if MACOSX_COREAUDIO
     AudioDeviceID deviceID;
+#else
+    SDL_bool interrupted;
+    CFTypeRef interruption_listener;
 #endif
 };