Enable color functions for ThemePicker

- Add color section for ThemePicker.
- Define theme stub apk with rainbow colors.
- Video:
  https://drive.google.com/file/d/1s_cpn1OegbD1Lof2PxaUVV08BTwpzimp/view

Flag: No impact to existing product: just moves code to AOSP for reference
Bug: 218396282
Test: Push apks with paths below & test.
 /system_ext/priv-app/ThemePicker/ThemePicker.apk
 /product/app/ThemesStub/ThemesStub.apk
Change-Id: I25130573ffb37075b4b71c6b83b7b903b6421ce3
diff --git a/themes/Android.bp b/themes/Android.bp
new file mode 100644
index 0000000..fb3d9be
--- /dev/null
+++ b/themes/Android.bp
@@ -0,0 +1,38 @@
+// Copyright (C) 2022 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 {
+    // See: http://go/android-license-faq
+    default_applicable_licenses: [
+        "Android-Apache-2.0",
+    ],
+}
+
+android_app {
+
+    name: "ThemesStub",
+    optimize: {
+        enabled: false,
+    },
+
+    aaptflags: ["--auto-add-overlay"],
+
+    sdk_version: "current",
+
+    product_specific: true,
+
+}
+
+// ==================================================