lib: expose v8.startupSnapshot functions on globalThis

[addaleax]

Not necessarily tied to this approach, but we've found this to be a genuine gap when trying to include libraries in startup snapshots. If we're reluctant to place these methods on the global object, I'd also consider the global process to be a good venue to expose this.

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Expose methods from require('v8').startupSnapshot which are relevant for isomorphic libraries through a Symbol-indexed property on the global object.

This provides a mechanism for using these functions from libraries that do not integrate with Node.js's module system, while still enabling integration with the startup snapshot mechanism. It also provides a path for exposing this feature from other runtimes that support a startup-snapshot-style feature.

We do not typically expose runtime-specific/non-standard capabilities on the global object, so using a Symbol property seems like the best way to avoid any potential naming conflicts and its consequences.

[joyeecheung]

I am a bit wary of adding things to globalThis. process would be a better compromise. Although if process is viable, then I think process.getBuiltinModule('v8').startupSnapshot also does the job? The API was specifically added to help isomorphic ESM feature-detect Node.js stuff.

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.69%. Comparing base (6df4f7b) to head (ffc4000).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_util.cc	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63138      +/-   ##
==========================================
+ Coverage   89.67%   89.69%   +0.01%     
==========================================
  Files         712      712              
  Lines      221251   221269      +18     
  Branches    42391    42397       +6     
==========================================
+ Hits       198405   198462      +57     
+ Misses      14669    14623      -46     
- Partials     8177     8184       +7     

Files with missing lines	Coverage Δ
lib/internal/process/pre_execution.js	98.03% <100.00%> (-0.36%)	⬇️
lib/internal/v8/startup_snapshot.js	95.80% <100.00%> (+0.31%)	⬆️
src/node_util.cc	80.65% <50.00%> (ø)

... and 29 files with indirect coverage changes

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