module: normalize package map paths

[Dansatch]

Package-map URLs ending with a slash, including ".." and "./", are stored differently from the paths used during lookup. This causes valid dependencies to fail with ERR_PACKAGE_MAP_EXTERNAL_FILE.

This change normalizes package paths when the map is loaded. Tests cover CommonJS, ESM, parent-directory URLs, trailing slashes, and duplicate paths.

The bug was reproduced on Node.js v26.8.2.

Fixes: #66043

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[github-actions]

Welcome to Node.js, and thank you for your first contribution!

Before review, please take a moment to read:

• the guide for first-time contributors
• the contribution and automation policies
• the pull request guide
• the AI use policy
• the Code of Conduct

Please make sure every commit is signed off. For a first pull request, GitHub Actions require collaborator approval and Jenkins CI must be started by a collaborator or triager, so an initial wait is normal.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.26%. Comparing base (bd2b98f) to head (40dc850).
⚠️ Report is 191 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66054      +/-   ##
==========================================
+ Coverage   90.25%   90.26%   +0.01%     
==========================================
  Files         789      789              
  Lines      271424   271424              
  Branches    51799    51801       +2     
==========================================
+ Hits       244964   244996      +32     
+ Misses      16931    16913      -18     
+ Partials     9529     9515      -14     

Files with missing lines	Coverage Δ
lib/internal/modules/package_map.js	100.00% <100.00%> (ø)

... and 22 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77607/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77706/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77724/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77873/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77888/

[nodejs-github-bot]

Landed in 0551dee