clipboard: include mime types in SDL_ClipboarUpdate

This patch modifies the clipboard handling so that when we receive an external
clipboard update, the suppported mime types are included in the SDL_ClipboarUpdate
event. The patch also introduces the owner field that allows to know if the update
is because we own the clipboard (internal update) or if it was an external update.

src/core/android/SDL_android.c

@@ -1377,7 +1377,8 @@ JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(onNativeAccel)(
 JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(onNativeClipboardChanged)(
     JNIEnv *env, jclass jcls)
 {
-    SDL_SendClipboardUpdate();
+    // TODO: compute new mime types
+    SDL_SendClipboardUpdate(false, NULL, 0);
 }
 
 // Low memory