Android: Finish EmulationActivity from C++

This makes EmulationActivity automatically close if booting
fails, and lets us get rid of s_emulation_end_event.

Source/Android/jni/AndroidCommon/IDCache.h

@@ -15,6 +15,7 @@ jmethodID GetDisplayAlertMsg();
 jmethodID GetDoRumble();
 jmethodID GetUpdateTouchPointer();
 jmethodID GetOnTitleChanged();
+jmethodID GetFinishEmulationActivity();
 
 jclass GetAnalyticsClass();
 jmethodID GetSendAnalyticsReport();