feat(developer): deploy kmc as ES module

Deploy kmc as an ES module, forced now by top-level await that we use in
the sentry load.

Moved NodeCompilerCallbacks to same util folder as schemas are found in,
to avoid rewriting schema loading with imports in this PR. It belongs
better there than messages/ anyway.

Distributed files are now .mjs. Removed --enable-source-maps from
launchers as logging will be managed with sentry anyway.