Support for targeting multiple worlds

It would be great to support the ability to create a component that can target the union of multiple worlds in the cases where the user cannot edit the wit file to create a third world that includes the target worlds. An example of this would be an SDK built on top of a wit that bundles the wit in an npm package and the user application wanting to target their world where there would be 2 distinct `wit` folders.

This request is motivated by the ability to do that in `componentize-py` (the [commit](https://github.com/bytecodealliance/componentize-py/commit/20787522a8822ae0ae7d9cdb18c6163cde9e7aac) that added the support).

The issue names no implementation files or tests. Start by reading the linked componentize-py commit and tracing how ComponentizeJS handles the distinct WIT folders described in the example. Done means ComponentizeJS can target the union of multiple worlds without requiring the user to edit the WIT file, with coverage for that scenario.

Written by the indexing model from the issue text.