fix: resolve alias in DTS output when unbundle is true

[joshuagraber]

Fixes #833

• This PR contains AI-generated code, but I have carefully reviewed it myself. Otherwise, my PR may be closed.
  • AI gen'd code limited to tests and refinement of what I wrote initially.

Description

Resolves issue where TS path aliases are not resolved with unbundle set to true.

Linked Issues

• Path aliases not resolved in DTS output with unbundle: true #833

Additional context

• baseUrl defaulting to . if it doesn't exist in the config is a risk, but should be a low one as TS path aliases require a baseUrl

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commit: f968f0f