Add the skeleton for the client-side API

android.system.virtualmachine is added as the client-side API for the
controlling of virtual machines. This change doesn't add any new API.
It adds an empty library to the existing framework.

Bug: 183496040
Test: atest MicrodroidHostTestCases
Change-Id: I9c52dfaf7e33137e5e3d6c587b5cc3932f667025
diff --git a/apex/Android.bp b/apex/Android.bp
index bbd4aa5..f06ff7a 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -50,6 +50,9 @@
         "vm",
         "compos_key_cmd",
     ],
+    java_libs: [
+        "android.system.virtualmachine",
+    ],
     prebuilts: [
         "com.android.virt.init.rc",
         "microdroid.json",