util: preserve function names without source map names

[privatenumber]

Problem

util.getCallSites({ sourceMap: true }) replaced a generated function name with an empty string when a valid source map omitted a name segment. Source-map names are optional, so tooling that consumes mapped call sites loses useful stack context.

For example, a generated foo() call mapped by a source map with an empty names array reported functionName: '' instead of functionName: 'foo'.

Changes

Preserve the V8 function name when the source map does not provide a replacement, matching Node.js's source-mapped stack-trace behavior. A regression fixture covers source maps with no name entries.

Fixes: #65104

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.31%. Comparing base (e2d7b34) to head (bdae980).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65108      +/-   ##
==========================================
- Coverage   90.31%   90.31%   -0.01%     
==========================================
  Files         759      759              
  Lines      248290   248289       -1     
  Branches    46859    46861       +2     
==========================================
- Hits       224241   224232       -9     
+ Misses      15472    15468       -4     
- Partials     8577     8589      +12     

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

... and 28 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/75631/