fix: enable stripInternal to avoid exposing type augmentations

[kirkwaiblinger]

PR Checklist

• Addresses an existing open issue: fixes 🐛 Bug: Emitted d.ts references internal only typescript types which causes errors in the d.ts file when typechecking #759
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.00%. Comparing base (4b3d274) to head (4bde943).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #765   +/-   ##
=======================================
  Coverage   61.00%   61.00%           
=======================================
  Files          35       35           
  Lines        2921     2921           
  Branches      463      463           
=======================================
  Hits         1782     1782           
  Misses       1139     1139           

Flag	Coverage Δ
4.8.4	58.61% <ø> (ø)
latest	60.32% <ø> (ø)

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[JoshuaKGoldberg]

👍

[JoshuaKGoldberg]

Released in ts-api-utils@2.1.1.