Add outputLength method

Test: build succeeds, `atest libinput-tests` passes.

Bug: 268245099

Change-Id: I030da703a907eef44e85d186144eddc53b5998cc
diff --git a/libs/input/TfLiteMotionPredictor.cpp b/libs/input/TfLiteMotionPredictor.cpp
index 3b061d1..85fa176 100644
--- a/libs/input/TfLiteMotionPredictor.cpp
+++ b/libs/input/TfLiteMotionPredictor.cpp
@@ -346,6 +346,10 @@
     return getTensorBuffer<const float>(mInputR).size();
 }
 
+size_t TfLiteMotionPredictorModel::outputLength() const {
+    return getTensorBuffer<const float>(mOutputR).size();
+}
+
 std::span<float> TfLiteMotionPredictorModel::inputR() {
     return getTensorBuffer<float>(mInputR);
 }