Make synstructure available to product and vendor am: ce999b0fc0 am: 53783e2b57 am: b39a0f6050

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

Change-Id: I925ed1b16807f37cf7c6cbad250d1c79803b46df
Signed-off-by: Automerger Merge Worker <[email protected]>