Expose TransformManager.getParent(int) (#3751)

It will be nice to have access to TransformManager EntityInstance parent.

android/filament-android/src/main/cpp/TransformManager.cpp

@@ -86,6 +86,13 @@ Java_com_google_android_filament_TransformManager_nSetParent(JNIEnv*, jclass,
             (TransformManager::Instance) newParent);
 }
 
+extern "C" JNIEXPORT jint JNICALL
+Java_com_google_android_filament_TransformManager_nGetParent(JNIEnv*, jclass,
+        jlong nativeTransformManager, jint i) {
+    TransformManager* tm = (TransformManager*) nativeTransformManager;
+    return tm->getParent((TransformManager::Instance) i).getId();
+}
+
 extern "C" JNIEXPORT void JNICALL
 Java_com_google_android_filament_TransformManager_nSetTransform(JNIEnv* env,
         jclass, jlong nativeTransformManager, jint i,

android/filament-android/src/main/java/com/google/android/filament/TransformManager.java

@@ -140,6 +140,19 @@ import androidx.annotation.Size;
         nSetParent(mNativeObject, i, newParent);
     }
 
+    /**
+     * Returns the actual parent entity of an {@link EntityInstance} originally defined
+     * by {@link #setParent(int, int)}.
+     *
+     * @param i the {@link EntityInstance} of the transform component to get the parent from.
+     * @return the parent {@link Entity}.
+     * @see #getInstance
+     */
+    @Entity
+    public int getParent(@EntityInstance int i) {
+        return nGetParent(mNativeObject, i);
+    }
+
     /**
      * Sets a local transform of a transform component.
      * <p>This operation can be slow if the hierarchy of transform is too deep, and this
@@ -241,6 +254,7 @@ import androidx.annotation.Size;
     private static native int nCreateArray(long mNativeObject, int entity, int parent, float[] localTransform);
     private static native void nDestroy(long nativeTransformManager, int entity);
     private static native void nSetParent(long nativeTransformManager, int i, int newParent);
+    private static native int nGetParent(long nativeTransformManager, int i);
     private static native void nSetTransform(long nativeTransformManager, int i, float[] localTransform);
     private static native void nGetTransform(long nativeTransformManager, int i, float[] outLocalTransform);
     private static native void nGetWorldTransform(long nativeTransformManager, int i, float[] outWorldTransform);