[api-extractor] API Extractor cannot resolve ambient modules

[zelliott]

Summary

If API Extractor is run on an entry point that re-exports a symbol from an ambient module, it's unable to resolve the ambient module, and thus throws an error.

Repro steps

1. Clone https://github.com/zelliott/rushstack/tree/ambient-modules
2. Run rush rebuild -o api-extractor-scenarios
3. Observe the error in the ambientModule test scenario.

InternalError: Internal Error: getResolvedModule() could not resolve module name "bar"
/Users/zell/Developer/rushstack/build-tests/api-extractor-scenarios/lib/ambientModule/index.d.ts:2:1

Details

The problem seems to be in the TypeScript getResolvedModule helper. It doesn't seem to be able to resolve ambient modules. It's not clear to me if there's something wrong in my setup, if there's a bug in getResolvedModule, or if API Extractor has to use some other TS compiler API to resolve ambient modules.

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
@microsoft/api-extractor version?	Latest
Operating system?	All
API Extractor scenario?	All
Would you consider contributing a PR?	Yes
TypeScript compiler version?	Latest
Node.js version (node -v)?	Latest

[iclanton]

This repros on this branch too: #3338

[zelliott]

Opened microsoft/TypeScript#48807 to get TS team's thoughts.