Make synstructure available to product and vendor am: ce999b0fc0 am: 53783e2b57

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/synstructure/+/2475390

Change-Id: I82c0af4beb4af6c3368a4ebd79ec914b924c9686
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>