Add microdroid demo app

Add a demo app showing how an app can start a VM.

Bug: N/A
Test: TARGET_BUILD_APPS=MicrodroidDemoApp m apps_only dist
adb install out/dist/MicrodroidDemoApp.apk
adb push out/dist/MicrodroidDemoApp.apk.idsig /data/local/tmp/virt/
adb root
adb shell start virtualizationservice
<then launch the app>

Change-Id: If46b2f8910b98b2b29ca0c629e1f7eacc01a477a
diff --git a/demo/res/values/themes.xml b/demo/res/values/themes.xml
new file mode 100644
index 0000000..16b8ab3
--- /dev/null
+++ b/demo/res/values/themes.xml
@@ -0,0 +1,16 @@
+<resources xmlns:tools="http://schemas.android.com/tools">
+    <!-- Base application theme. -->
+    <style name="Theme.MicrodroidDemo" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
+        <!-- Primary brand color. -->
+        <item name="colorPrimary">@color/purple_500</item>
+        <item name="colorPrimaryVariant">@color/purple_700</item>
+        <item name="colorOnPrimary">@color/white</item>
+        <!-- Secondary brand color. -->
+        <item name="colorSecondary">@color/teal_200</item>
+        <item name="colorSecondaryVariant">@color/teal_700</item>
+        <item name="colorOnSecondary">@color/black</item>
+        <!-- Status bar color. -->
+        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
+        <!-- Customize your theme here. -->
+    </style>
+</resources>