Migrate to cargo_embargo. am: 09fa908e3c am: 13258ba725 am: ebe79e71f0

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

Change-Id: I795698524f7d56608adc06e9f5080ca94fc37d13
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>