Migrate to cargo_embargo. am: 17c785e114 am: 3f51dd0bc9

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro2/+/2830192

Change-Id: Ib8e0a6b0685f81da93a41f3d6c5d1bd3d5dbd6ad
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>