Define and implement a service for key management in CompOS.

This is based on the interface prototyped in
system/security/ondevice-signing/FakeCompOs.h.

For now, to allow manual testing, this is a standalone binary.

Bug: 191763370
Test: Builds.
Change-Id: I307ba9144fa51cca7ebee2142980f3a1cd436ef2
diff --git a/compos/aidl/Android.bp b/compos/aidl/Android.bp
index 3639775..07bec09 100644
--- a/compos/aidl/Android.bp
+++ b/compos/aidl/Android.bp
@@ -15,5 +15,10 @@
                 "com.android.compos",
             ],
         },
+        ndk: {
+            apex_available: [
+                "com.android.virt",
+            ],
+        },
     },
 }