Merge "Allow generated source to be root module src." am: 69cd8ed5c5 am: b5c54b485c

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/protobuf-codegen/+/1412814

Change-Id: I7ef5c7168cbd9d7b98294615e02db6aea3d8f17a