Migrate to cargo_embargo. am: 09fa908e3c am: 3ab97caee8 am: 3be671ef65

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/hex/+/2826431

Change-Id: I8726584882df21e1f6d290995b7e64536b88eb47
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>