worker: add Symbol.toStringTag to messaging classes

[lazerg]

MessageChannel, MessagePort and BroadcastChannel had no
Symbol.toStringTag, so Object.prototype.toString.call() returned
[object Object] or [object EventTarget] rather than the interface
names.

Two existing tests expected util.inspect() to print
MessagePort [EventTarget]; the tag now matches the constructor name,
so the bracketed part is gone.

Fixes: #65527

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.65%. Comparing base (4b5e86c) to head (070a5ec).
⚠️ Report is 435 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65532      +/-   ##
==========================================
+ Coverage   90.14%   91.65%   +1.51%     
==========================================
  Files         751      789      +38     
  Lines      253679   285455   +31776     
  Branches    47789    69104   +21315     
==========================================
+ Hits       228671   261635   +32964     
+ Misses      16264    14430    -1834     
- Partials     8744     9390     +646     

Files with missing lines	Coverage Δ
lib/internal/worker/io.js	99.23% <100.00%> (+0.03%)	⬆️

... and 283 files with indirect coverage changes

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[brettz9]

Could the failure be flake, remedied by another test run?

[lazerg]

The failure does not come from this change. wpt/test-web-locks crashed on macOS after all of its subtests passed. That matches the known flake in #59142, where held.https.any.js throws an expected rejection and the harness does not register it. test/wpt/status/web-locks.json already marks that file flaky, and its note covers ppc, linux x64 and s390x only. The same commit passed test-linux on both arches, which runs the same WPT suite, and my diff only defines Symbol.toStringTag on the three messaging classes. A new run should come back green, but I cannot start one here.