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.
Fixes#7408.
For kmc*.cmd, enables source maps. If you are running kmc from node on
your own system, you may need to enable source maps in other ways.
Note that error reports should be going through to Sentry, and source
maps should already be used for those.