Legacy generated code compatibility smoke test

This directory contains a smoke unit tests that runs the core functionality of generated code against the latest runtime.

Note that running protoc as a build step rather than checking in gencode is the strongly recommended pattern, and any Bazel users should use proto_library() rules to achieve that rather than checking in generated code.

This directory is only using checked in generated code as the mechanism to test the compatibility with stale gencode created by an older protoc, which is expected to be relevant in non-Bazel usecases where it may be difficult to run protoc at build time.