src: apply IsolateSettings when using a snapshot

[codebytere]

When NewIsolate() is given snapshot data it applies only the misc half of IsolateSettings and leaves the error handlers for later; CreateEnvironment() then installs them with default settings once the main context is deserialized. So with a snapshot, an embedder's fatal_error_callback, oom_error_callback, should_abort_on_uncaught_exception_callback and prepare_stack_trace_callback are dropped, and the message listener is added even if MESSAGE_LISTENER_WITH_ERROR_LEVEL was cleared. The only workaround is calling SetIsolateUpForNode() again after CreateEnvironment().

This makes NewIsolate() apply all of the settings whether or not there is snapshot data, as its comment in node.h already says, and CreateEnvironment() stops touching isolate handlers. The deferral came in with #27321, but every handler copes with there being no Environment yet (without a snapshot they have always been installed before any context exists), and workers already call SetIsolateUpForNode() straight after a snapshot NewIsolate(), so that call goes too.

Tests: embedtest gets an --embedder-isolate-settings mode that goes through NewIsolate()/CreateIsolateData()/CreateEnvironment() with a custom prepare_stack_trace_callback, since CommonEnvironmentSetup takes no settings; the new test-embedding-snapshot-isolate-settings.js checks that callback still formats new Error().stack once the Environment is created from a snapshot; it fails on main and passes here. Embedding suite, cctest and the default suite pass.

Refs: #27321
Refs: #45888

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Disclosure: the code, test and this description were written by Claude Code, directed and reviewed by @codebytere.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (03fb384) to head (1e39848).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65407      +/-   ##
==========================================
+ Coverage   90.10%   90.12%   +0.01%     
==========================================
  Files         752      752              
  Lines      252209   252201       -8     
  Branches    47454    47446       -8     
==========================================
+ Hits       227260   227289      +29     
+ Misses      16264    16215      -49     
- Partials     8685     8697      +12     

Files with missing lines	Coverage Δ
src/api/environment.cc	78.09% <100.00%> (-0.18%)	⬇️
src/node_internals.h	80.35% <ø> (ø)
src/node_worker.cc	81.69% <ø> (-0.13%)	⬇️

... and 35 files with indirect coverage changes

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