Add optional timeout to PropertyWatcher::wait. am: 9349cf0598 am: 6bf2d6abc3

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

Change-Id: I873eba36339344c46a1a3453f7ce5543e58a755e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>