Fixed asset_manager.h, rect_manager.h, and jni.h

1. Fixed missing #include <sys/types.h> in android/asset_manager.h for API >= 13
2. Fixed missing #include <stdint.h> in android/rect_manager.h for API >= 14
3. Added JNICALL to JNI_OnLoad and JNI_OnUnload in jni.h

Change-Id: I875ec0b6e6f7c2f433c176f0a738eb78f3c33062

ndk/platforms/android-14/include/android/rect.h

@@ -18,6 +18,8 @@
 #ifndef ANDROID_RECT_H
 #define ANDROID_RECT_H
 
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif