Copying the ARCore for Jetpack XR Whitebox test app to AndroidX.

The Gradle, XML and asset files were manually copied. The Kotlin
code was automatically copied via the migration script.

Creating a bespoke assets directory so these files can be shared
across all XR libraries.

Test: Validated the application on device.
Change-Id: If9653dacf61f0e7bb98d81c78ad80a6e2625b617
Bug: 389160446
diff --git a/xr/assets/build.gradle b/xr/assets/build.gradle
new file mode 100644
index 0000000..0116f70
--- /dev/null
+++ b/xr/assets/build.gradle
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2024 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.
+ */
+
+/**
+ * This file was created using the `create_project.py` script located in the
+ * `<AndroidX root>/development/project-creator` directory.
+ *
+ * Please use that script when creating a new project, rather than copying an existing project and
+ * modifying its settings.
+ */
+
+import androidx.build.LibraryType
+
+plugins {
+    id("AndroidXPlugin")
+    id("com.android.library")
+    id("org.jetbrains.kotlin.android")
+}
+
+android {
+    namespace = "androidx.xr.assets"
+}
+
+androidx {
+    name = "XR Assets"
+    type = LibraryType.INTERNAL_TEST_LIBRARY
+    inceptionYear = "2024"
+    description = "Collection of assets for use across the XR libraries."
+}