src: dump snapshot source with node:generate_default_snapshot_source

[joyeecheung]

This helps diffing snapshots when the reproducibility gets broken.

[nodejs-github-bot]

Review requested:

• @nodejs/startup

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.51%. Comparing base (4f24aff) to head (09ccbcf).
⚠️ Report is 78 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61101      +/-   ##
==========================================
- Coverage   88.53%   88.51%   -0.02%     
==========================================
  Files         703      703              
  Lines      208546   208552       +6     
  Branches    40217    40221       +4     
==========================================
- Hits       184634   184601      -33     
- Misses      15926    15944      +18     
- Partials     7986     8007      +21     

Files with missing lines	Coverage Δ
src/node.cc	75.96% <100.00%> (-0.08%)	⬇️

... and 42 files with indirect coverage changes

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[joyeecheung]

Removed the unused file and added back the helper (turns out it's still used to format stderr during failures).

[github-actions]

Failed to start CI

   ⚠  Commits were pushed since the last approving review:
   ⚠  - src: dump snapshot source with node:generate_default_snapshot_source
   ⚠  - fixup! src: dump snapshot source with node:generate_default_snapshot_…
   ⚠  - fixup! fixup! src: dump snapshot source with node:generate_default_sn…
   ✘  Refusing to run CI on potentially unsafe PR

https://github.com/nodejs/node/actions/runs/20415476248

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70649/