Add demo apk for car support lib.

Screenshot: https://screenshot.googleplex.com/qOfF4iBox87

Test: Run through android studio. Also installation with gradle:
./gradlew :support-car-demos:installDebug

BUG: 69572465

Change-Id: I445f31da59e4c9ec4a63b0069fb47a96211b3789
diff --git a/settings.gradle b/settings.gradle
index 0544c91..1eccbcf 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -165,6 +165,8 @@
 include ':support-emoji-demos'
 project(':support-emoji-demos').projectDir = new File(samplesRoot, 'SupportEmojiDemos')
 
+include ':support-car-demos'
+project(':support-car-demos').projectDir = new File(samplesRoot, 'SupportCarDemos')
 /////////////////////////////
 //
 // Testing libraries