switch to esm-only with development condition enabling dev-instanceOf-check

[yaacovCR]

Takes the no-op trick from #4426, but responding in a small way to feedback from @glasser in terms of discoverability, uses the development condition to enable this behavior by default.

The development condition must be passed to node via a flag node --conditions=development ... and is not set automatically from NODE_ENV=development.

[yaacovCR]

where we get the import-only warning, we are actually relying on esm-require

[yaacovCR]

Closing in favor of #4464