Adding @hide to UpdateEngineStable

Adding hide annotation to ue stable APIs and updating interface version.
Freezing interface with version 2.

Test: m libupdate_engine_stable-V2-java
Bug: 317914533

Change-Id: Ice7d095b9a6903754ab76e1e097d941773119508
diff --git a/stable/Android.bp b/stable/Android.bp
index 54ae35d..aed493a 100644
--- a/stable/Android.bp
+++ b/stable/Android.bp
@@ -49,7 +49,18 @@
             ],
         },
     },
-    versions: ["1"],
+    versions_with_info: [
+        {
+            version: "1",
+            imports: [],
+        },
+        {
+            version: "2",
+            imports: [],
+        },
+    ],
+    frozen: true,
+
 }
 
 // update_engine_stable_client (type: executable)