Support Import map placeholders for monorepo modules

[dogukanakkaya]

For monorepo modules like aws-sdk, especially the ones that keeps the same versions for all monorepos regarding it's changed or not. We have to keep defining every submodule we will use in import map.

Example from aws-sdk. We have all different clients under @aws-sdk. To add specific versions of those in import map I have to explicitly add all of these with same versions again and again.

"aws-sdk/client-ses": "npm:@aws-sdk/client-ses@3.391.0",
"aws-sdk/client-sqs": "npm:@aws-sdk/client-sqs@3.391.0",
"aws-sdk/client-s3": "npm:@aws-sdk/client-s3@3.391.0"

Instead we can define this once with a placeholder for client-ses, client-sqs etc. Like:

"aws-sdk/$1": "npm:@aws-sdk/$1@3.391.0"

And then this can be used in the app like:

import { ... } from "aws-sdk/client-sqs"

Also Babel is the same but I guess submodules inside that may have different versions. Anyways, aws-sdk is a good case for this. But I am not sure if this is very relevant at the moment or would have any different use cases.