Upgrade rust/crates/protobuf to 2.18.1 am: 4bf8b46757 am: 1a266ee5bb am: 762d4424d1

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/protobuf/+/1510524

Change-Id: Idbd6cc8c039cad3f26b0cb8b9fe4a51c00b49008
tree: 268f7e94ca5929b460ed2bea90c8ea92a44406f7
  1. benches/
  2. out/
  3. src/
  4. .cargo_vcs_info.json
  5. Android.bp
  6. build.rs
  7. Cargo.toml
  8. Cargo.toml.orig
  9. LICENSE.txt
  10. METADATA
  11. MODULE_LICENSE_MIT
  12. OWNERS
  13. README.md
  14. regenerate.sh
  15. TEST_MAPPING
README.md

How to develop rust-protobuf itself

cargo test --all to build everything.

If code generator is changed, code needs to be regenerated, see regenerate.sh.