Add aidl_interface for update_engine

Enables the rust backend for the IUpdateEngine interface.

Test: Add a dependant binary and build with "m"
Change-Id: I54fca9fc59963b58ff6f6ee68d9fc41ead5fde5a
diff --git a/Android.bp b/Android.bp
index 0cbf286..89dea90 100644
--- a/Android.bp
+++ b/Android.bp
@@ -503,6 +503,29 @@
     ],
 }
 
+aidl_interface {
+    name: "libupdate_engine_aidl_interface",
+    srcs: [
+        ":libupdate_engine_aidl",
+    ],
+    backend: {
+        cpp: {
+            enabled: false,
+        },
+        java: {
+            enabled: false,
+        },
+        ndk: {
+            enabled: false,
+        },
+        rust: {
+            enabled: true,
+        },
+    },
+    frozen: false,
+    unstable: true,
+}
+
 cc_defaults {
     name: "libupdate_engine_android_defaults",
     defaults: [