[Thread] add demoapp for Thread network APIs

A screenshot of the demo app:
![](https://screenshot.googleplex.com/AsiYKPzG4nJpr6x.png)

Bug: 273227725
Change-Id: I8d9bcf00bb54d3f152c436b56df919d967c5b71b
diff --git a/thread/demoapp/res/values/dimens.xml b/thread/demoapp/res/values/dimens.xml
new file mode 100644
index 0000000..5165951
--- /dev/null
+++ b/thread/demoapp/res/values/dimens.xml
@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2023 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.
+-->
+
+<resources>
+  <!-- Default screen margins, per the Android Design guidelines. -->
+  <dimen name="activity_horizontal_margin">16dp</dimen>
+  <dimen name="activity_vertical_margin">16dp</dimen>
+  <dimen name="nav_header_vertical_spacing">8dp</dimen>
+  <dimen name="nav_header_height">176dp</dimen>
+  <dimen name="fab_margin">16dp</dimen>
+</resources>