Add optional timeout to PropertyWatcher::wait. am: 9349cf0598

Original change: https://android-review.googlesource.com/c/platform/system/librustutils/+/2584503

Change-Id: Ide9c3f66eeabd3eb3ed76fd50d88b739261a1578
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>