Add syntax & type check for Node.js example on CI

[Johennes]

This uses node --check and tsc to perform some basic syntax and type checking on the Node.js example.

It's slightly odd to have this running on every PR when the JS SDK version is pinned in the example's package.json. If we find a way to update the JS SDK in the example via renovate, maybe we could switch the CI to use the local SDK instead?

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).

[richvdh]

lgtm