test_runner: mock dual-package with conditional exports

[maruthang]

When mock.module() targets a package whose exports field maps
import and require to different files, the ESM resolver and the
CJS resolver disagree on the resolved path. Only the ESM path was
registered in mockMap, so require() of the mocked specifier
bypassed the mock and loaded the real CJS module.

Resolve the specifier through Module._resolveFilename from the
caller's directory in addition to the existing ESM resolution. When
the two paths differ, register the CJS path as a second key in
mockMap and invalidate Module._cache[cjsPath], restoring it on
restore(). Single-resolution packages keep their existing behavior.

Note: I was unable to run the test suite locally (no built out/Release/node available on this Windows host). All four files pass node --check; the resolver-divergence premise was verified empirically against system Node. Looking forward to CI verification.

Fixes: #58231

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[codecov]

Codecov Report

❌ Patch coverage is 82.95455% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.64%. Comparing base (4744070) to head (8c4a8e4).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/test_runner/mock/mock.js	82.95%	13 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62943      +/-   ##
==========================================
- Coverage   89.66%   89.64%   -0.03%     
==========================================
  Files         706      706              
  Lines      219370   219489     +119     
  Branches    42065    42095      +30     
==========================================
+ Hits       196694   196751      +57     
- Misses      14586    14638      +52     
- Partials     8090     8100      +10     

Files with missing lines	Coverage Δ
lib/internal/test_runner/mock/mock.js	97.53% <82.95%> (-1.28%)	⬇️

... and 49 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.

[JakobJingleheimer]

Thanks for this! The tests is correct, and I see it's passing.

I'll do a pass on the implementation soon.

I can't remember whether http/s specifiers are still supported (I think that was maybe removed?).