src: fix task queue deadlock when built as C++23

[codebytere]

Refs: #65353

Since #65353, FlushForegroundTasksInternal() and the worker DelayedTaskScheduler drain their queues with for (auto& task : queue.Lock().PopAll()). In C++20 the Locked temporary is destroyed at the end of the range initializer, before the loop body runs. C++23 (P2718R0) extends the lifetime of every temporary in a range-for initializer to the end of the loop, so the queue's mutex stays held while the tasks run, and the first task that posts to the same queue - any V8 foreground task that schedules another one - deadlocks on the non-recursive mutex. Node.js itself builds with -std=gnu++20 and is unaffected today, but an embedder that compiles it as C++23 hangs in the first foreground task flush, and so will Node.js once common.gypi moves on.

This stores the drained tasks in a local before iterating at the three sites, so the lock is released independent of the language version, and notes the constraint on PopAll(). No new test: PlatformTest.SkipNewTasksInFlushForegroundTasks already posts a foreground task from inside a flushed one and deadlocks under a C++23 build without this change; verified with a clang 20 -std=gnu++23 build of main before (hangs in test-worker-arraybuffer-zerofill and that cctest) and after (passes), plus the regular gcc C++20 build.

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Disclosure: the code 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 90.26%. Comparing base (67e66b8) to head (8e9431e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66066      +/-   ##
==========================================
- Coverage   90.27%   90.26%   -0.01%     
==========================================
  Files         789      789              
  Lines      271473   271475       +2     
  Branches    51808    51806       -2     
==========================================
- Hits       245066   245045      -21     
- Misses      16880    16897      +17     
- Partials     9527     9533       +6     

Files with missing lines	Coverage Δ
src/node_platform.cc	75.04% <100.00%> (+0.09%)	⬆️
src/node_platform.h	85.71% <ø> (ø)

... and 28 files with indirect coverage changes

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