Replace existing Robolectric test task with functioning one.

This CL does the following:
- Creates a dir for multivalentTests
- Creates symlinks for the dir to keep Android Studio happy
- Moves many files to the multivalentTests dir
- Adjusts gradle and soong build files to use the new dir as part of
their source sets.

Test: ./gradlew :NexusLauncher:testGoogleWithQuickstepDebugUnitTest
Test: atest Launcher3RoboTests
Fix: 316553886
Bug: 316553889
Flag: NA
Change-Id: Iae28fd0c0191b3ecf9bd2950800875950cca2622

tests/multivalentTests/dummy_app/src/com/example/android/aardwolf/Activity1.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.example.android.aardwolf;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.view.View;
+
+public class Activity1 extends Activity {
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        View view = getLayoutInflater().inflate(R.layout.empty_activity, null);
+        setContentView(view);
+    }
+}
+