Separate MediaRouter Androidx demo to a new app.

- Remove some extra un-related work like light/dark themes, ...etc.

Bug: 257999945
Test: Manually
Change-Id: I2d3f11d39402ce9a22d452f07dc3d72cbdc7349f
diff --git a/settings.gradle b/settings.gradle
index afcd43e..4e3b1e2 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -982,6 +982,7 @@
 // Note: don't add new samples/ apps. Instead, Create
 // <module>/integration-tests/testapp in the "Libraries" section above.
 includeProject(":androidx-demos", new File(samplesRoot, "AndroidXDemos"), [BuildType.MAIN])
+includeProject(":media-routing-demo", new File(samplesRoot, "MediaRoutingDemo"), [BuildType.MAIN])
 includeProject(":support-animation-demos", new File(samplesRoot, "SupportAnimationDemos"), [BuildType.MAIN])
 includeProject(":support-content-demos", new File(samplesRoot, "SupportContentDemos"), [BuildType.MAIN])
 includeProject(":support-emoji-demos", new File(samplesRoot, "SupportEmojiDemos"), [BuildType.MAIN])