sea: implement sea.getAssetKeys()

[joyeecheung]

This adds a new API to allow the bundled script in SEA to query the list of assets.

Refs: nodejs/single-executable#112

[nodejs-github-bot]

Review requested:

• @nodejs/single-executable

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.89%. Comparing base (bcb802c) to head (2e32631).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_sea.cc	76.47%	1 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #59661      +/-   ##
==========================================
- Coverage   89.91%   89.89%   -0.03%     
==========================================
  Files         667      667              
  Lines      196600   196631      +31     
  Branches    38601    38604       +3     
==========================================
- Hits       176780   176766      -14     
- Misses      12269    12319      +50     
+ Partials     7551     7546       -5     

Files with missing lines	Coverage Δ
lib/sea.js	98.88% <100.00%> (+0.20%)	⬆️
src/node_sea.cc	86.20% <76.47%> (-0.31%)	⬇️

... and 33 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/68948/