Maybe add Status.withCode

Unlike other fields in Status, there is no `with` method to preserve the code. This is surprising and makes it harder to change a status code.

Would have been useful here: https://github.com/grpc/grpc-java/pull/3521/files

Start by locating the Java gRPC Status API and review the referenced pull request for how other Status fields expose with methods. Confirm the expected behavior for preserving the code when changing a status, then add the corresponding API coverage and verify the existing tests pass.

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