Migrate to cargo_embargo. am: ef64a94361 am: 83a5ae1063

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/slab/+/2833050

Change-Id: I57583bf0978cbee4381eaa3a0380c785bcd817de
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>