Test paths used in configuration loader

[jsjoeio]

Follow-up item from #3760

Testing the paths like this might not catch anything since we'd be copying any mistakes we already have.

The ideal might be to:

1. Ensure that each path resolves to a real Node module.
2. Check VS Code's workbench.html and make sure we have the same paths we do (maybe could do this later).

@code-asher

[stale]

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