Add support for dynamic import maps

[yoavweiss]

What is the problem this feature will solve?

Import maps currently have to load before any ES module and there can only be a single import map per document. That makes them fragile and potentially slow to use in real-life scenarios: Any module that loads before them breaks the entire app, and in apps with many modules the become a large blocking resource, as the entire map for all possible modules needs to load first.

What is the feature you are proposing to solve the problem?

There's an HTML PR proposal to enable multiple import maps per document, by merging them in a consistent and deterministic way.

I'd appreciate y'all's opinions.

What alternatives have you considered?

No response

[benjamingr]

We haven't even added regular import maps, there is a feature request somewhere but users/core doesn't seem to prioritize it in a Node.js setting since we don't have many of the problems browsers have and we have a lot more tools for resolution already.

cc @nodejs/loaders @nodejs/web-standards