First class modules and dynamic import

[cometkim]

ReScript's dynamic import feature is not really "dynamic"; it's just a lazy import of a static module.

We haven't caught up with ESM yet, which allows us to change the program remotely via different modules. This is a must-have feature for use cases like plugins or mini apps.

Dynamic import is one of the older use cases for first-class module syntax,
https://github.com/shakacode/rescript-first-class-modules-usage

But I'd like to see it supported natively in ESM.