[android] android gradle project for ops (#2897)

* [android] android gradle project for ops

* Change CMakeLists to latest PyTorch

* Use mobilenet_v3 models for detection

Don't need to have two variants of the model anymore, but I'm not removing it for now

* Fix orientation when angle = 0

* [android][test_app] Fix YUV decoding

* Use smaller version of mobilenet model

* Divide inputs by 255 again

* [android] assets mobilenetv3
Co-authored-by: Francisco Massa <fvsmassa@gmail.com>

android/test_app/app/src/main/res/layout/activity_camera.xml

+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout
+        xmlns:android="http://schemas.android.com/apk/res/android"
+        xmlns:tools="http://schemas.android.com/tools"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        tools:context=".CameraActivity">
+
+    <ViewStub
+            android:id="@+id/camera_texture_view_stub"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:layout="@layout/texture_view"/>
+
+    <TextView
+            android:id="@+id/text"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:layout_gravity="top"
+            android:textSize="16sp"
+            android:textStyle="bold"
+            android:textColor="#ff0000"/>
+
+    <ImageView
+            android:id="@+id/camera_overlay"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"/>
+</FrameLayout>

android/test_app/app/src/main/res/layout/activity_main.xml

+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    tools:context=".MainActivity">
+
+    <TextView
+        android:id="@+id/text"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:layout_gravity="top"
+        android:textSize="14sp"
+        android:background="@android:color/black"
+        android:textColor="@android:color/white" />
+
+</FrameLayout>
\ No newline at end of file

android/test_app/app/src/main/res/layout/texture_view.xml

+<?xml version="1.0" encoding="utf-8"?>
+<TextureView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/texture_view"
+    android:layout_width="match_parent"
+    android:layout_height="0dp" />

android/test_app/app/src/main/res/values/colors.xml

+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="colorPrimary">#008577</color>
+    <color name="colorPrimaryDark">#00574B</color>
+    <color name="colorAccent">#D81B60</color>
+</resources>

android/test_app/app/src/main/res/values/strings.xml

+<resources>
+    <string name="app_name">TV_FRCNN</string>
+</resources>

android/test_app/app/src/main/res/values/styles.xml

+<resources>
+
+    <!-- Base application theme. -->
+    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
+        <!-- Customize your theme here. -->
+        <item name="colorPrimary">@color/colorPrimary</item>
+        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
+        <item name="colorAccent">@color/colorAccent</item>
+    </style>
+
+</resources>

android/test_app/make_assets.py

+import torch
+import torchvision
+from torch.utils.mobile_optimizer import optimize_for_mobile
+
+print(torch.__version__)
+
+model = torchvision.models.detection.fasterrcnn_mobilenet_v3_large_320_fpn(
+    pretrained=True,
+    box_score_thresh=0.7,
+    rpn_post_nms_top_n_test=100,
+    rpn_score_thresh=0.4,
+    rpn_pre_nms_top_n_test=150)
+
+model.eval()
+script_model = torch.jit.script(model)
+opt_script_model = optimize_for_mobile(script_model)
+opt_script_model.save("app/src/main/assets/frcnn_mnetv3.pt")

torchvision/csrc/vision.cpp

 #include "vision.h"
 
+#ifndef MOBILE
 #include <Python.h>
+#endif
 #include <torch/library.h>
 
 #ifdef WITH_CUDA