Run abandon() in the system server context

abandon() will call into StagingManager which might
trigger external callbacks. The code should not
run in the context of the calling uid.

Bug: 267383992
Test: CtsStagedInstallHostTestCases
Change-Id: Ib8a1b6bd48388e1dc2362b8f7cbe4c0d41ee3ebc

services/core/java/com/android/server/pm/PackageInstallerSession.java

@@ -3995,7 +3995,14 @@ public class PackageInstallerSession extends IPackageInstallerSession.Stub {
                 return;
             }
         }
-        r.run();
+
+        final long token = Binder.clearCallingIdentity();
+        try {
+            // This will call into StagingManager which might trigger external callbacks
+            r.run();
+        } finally {
+            Binder.restoreCallingIdentity(token);
+        }
     }
 
     @Override