Adopt polyglot example

Mixed tree with a Python package, a Rust crate, a JavaScript package, a TypeScript package, and a C++ library with a handwritten binary in its own child package.

bazel run @rules_dx//:dx -- init //examples/adopt-polyglot/...
bazel run @rules_dx//:dx -- generate //examples/adopt-polyglot/...
bazel build //examples/adopt-polyglot/...
bazel test //examples/adopt-polyglot/...

All 4 tests pass (shapes_test, widgets_test, totals_test, native_test). The TypeScript wrapper emits its own typecheck tests, so bazel test runs more targets than the example declares.