Correct vulnerability when setting pending intents on import/export...

Correct vulnerability when setting pending intents on import/export notifications by setting FLAG_IMMUTABLE am: 1d595f80 am: 835bc188 am: 2aedd25d am: b19ebd07 am: f24d838e am: 10a03e71 am: f8fc2fda am: fb9cc15e am: 8c686f48

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Contacts/+/12272170

Change-Id: I14c3fe2677e06d9f3c864979de4e103dbd78612d