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 90.12%. Comparing base (4b5e86c) to head (070a5ec).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65532      +/-   ##
==========================================
- Coverage   90.14%   90.12%   -0.02%     
==========================================
  Files         751      751              
  Lines      253679   253657      -22     
  Branches    47789    47790       +1     
==========================================
- Hits       228671   228606      -65     
- Misses      16264    16311      +47     
+ Partials     8744     8740       -4     

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

... and 42 files with indirect coverage changes

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