Add API to track package changes

After any package install, removal or update, save the changed
package and update a global sequence number. At any point, apps
can query for the packages changed since a particular sequence
number.

If a package is changed multiple times, it is only included once
in the change list.

Bug: 33865505
Test: Create sample app to query for changes and see which packages are changed after performing certain operations
Change-Id: Ia4646035362b16a97110e05f3f909ce385b48428
diff --git a/core/java/android/app/ApplicationPackageManager.java b/core/java/android/app/ApplicationPackageManager.java
index 0c6c4ba..333e412 100644
--- a/core/java/android/app/ApplicationPackageManager.java
+++ b/core/java/android/app/ApplicationPackageManager.java
@@ -29,6 +29,7 @@
 import android.content.IntentSender;
 import android.content.pm.ActivityInfo;
 import android.content.pm.ApplicationInfo;
+import android.content.pm.ChangedPackages;
 import android.content.pm.ComponentInfo;
 import android.content.pm.InstantAppInfo;
 import android.content.pm.FeatureInfo;
@@ -506,6 +507,15 @@
     }
 
     @Override
+    public ChangedPackages getChangedPackages(int sequenceNumber) {
+        try {
+            return mPM.getChangedPackages(sequenceNumber, mContext.getUserId());
+        } catch (RemoteException e) {
+            throw e.rethrowFromSystemServer();
+        }
+    }
+
+    @Override
     @SuppressWarnings("unchecked")
     public FeatureInfo[] getSystemAvailableFeatures() {
         try {