ml: prepare for loading libhandwriting.so from dlc.

(1) use flag nodevice_handwriting_dlc is passed to mlservice.

(2) libhandwriting.so is moved to model_path.

(3) GetModelPaths is moved inside handwriting.cc.

(4) Fixed all unit tests to use the default model_path on the rootfs.

BUG=chromium:1054628
TEST='All unit tests passed.'

Cq-Depend: chromium:2331385,chromium:2332072
Change-Id: I35afa96d221cafa8951528365dd53424602833d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2325512
Reviewed-by: Charles . <charleszhao@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Andrew Moylan <amoylan@chromium.org>
Tested-by: Charles . <charleszhao@chromium.org>
Commit-Queue: Charles . <charleszhao@chromium.org>
diff --git a/ml/machine_learning_service_impl.h b/ml/machine_learning_service_impl.h
index 62b8966..3a7acba 100644
--- a/ml/machine_learning_service_impl.h
+++ b/ml/machine_learning_service_impl.h
@@ -56,15 +56,12 @@
       mojo::PendingReceiver<chromeos::machine_learning::mojom::TextClassifier>
           receiver,
       LoadTextClassifierCallback callback) override;
-  void LoadHandwritingModel(
-      mojo::PendingReceiver<
-          chromeos::machine_learning::mojom::HandwritingRecognizer> receiver,
-      LoadHandwritingModelCallback callback) override;
+  void RemovedFunction_3() override;
   void LoadHandwritingModelWithSpec(
       chromeos::machine_learning::mojom::HandwritingRecognizerSpecPtr spec,
       mojo::PendingReceiver<
           chromeos::machine_learning::mojom::HandwritingRecognizer> receiver,
-      LoadHandwritingModelCallback callback) override;
+      LoadHandwritingModelWithSpecCallback callback) override;
 
   // Init the icu data if it is not initialized yet.
   void InitIcuIfNeeded();