Add rust_test and update TEST_MAPPING am: 35dedf6a77 am: ff20eba123 am: e6fcd6b3bb

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/protobuf-codegen/+/1365084

Change-Id: I6bea8abf10b364b405522d53d49dc033d0abfc42