getReferencedSourceFiles does not return paths from custom path mapping

**Is your feature request related to a problem? Please describe.**

```typescript
const c = project.getSourceFiles().map((a) => a.getReferencedSourceFiles());
```

Will only return relative file references. For example https://github.com/microsoft/vscode/blob/main/src/tsconfig.base.json#L16, and files imported using this custom path will not show in results.

The file I am testing is https://github.com/microsoft/vscode/blob/main/src/vs/editor/editor.main.ts, which will have _no_ results.

**Describe the solution you'd like**

Return all references.

**Describe alternatives you've considered**

I don't know of a good alternative.

Side note: I am trying to navigate from one source file to another based on import paths. If someone has a good solution here, I am all ears.

Reproduce the issue with src/vs/editor/editor.main.ts and the custom path mapping in src/tsconfig.base.json, starting from getReferencedSourceFiles(). Trace how mapped imports are resolved and verify that the method returns both relative and custom-mapped references. There are no implementation files or tests named in the issue.

Written by the indexing model from the issue text.