feat: add ConstructorTraitTag to allow constructor return overridding

[legendecas]

Fixes: #1661

• Add docs.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.79%. Comparing base (a6213bb) to head (d07f9d7).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
napi-inl.h	40.00%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1670   +/-   ##
=======================================
  Coverage   65.79%   65.79%           
=======================================
  Files           3        3           
  Lines        2146     2149    +3     
  Branches      715      716    +1     
=======================================
+ Hits         1412     1414    +2     
  Misses        162      162           
- Partials      572      573    +1     

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[legendecas]

This does not work for InstanceMethod because there is a branch check enabled at https://github.com/nodejs/node/blob/main/src/js_native_api_v8.cc#L1028.

[greggman]

Thank you for working on this!

It's not clear from the comments if this is working yet. It sounds like maybe not?

I would suggest adding a few more tests

• Make a C++ class that inherits from Event, then pass it to a native event target

  const myEvent = new CPPClassThatInheritsFromEvent('nameOfEvent');
  const target = new EventTarget();
  const e = await new Promise(resolve => {
    target.addEventListener('nameOfEvent', resolve, { once: true });
    target.dispatchEvent(myEvent);
  });
  assert(e === myEvent);

• Make a C++ class that inherits from EventTarget. Maybe sure you can use EventTarget's functionality

  const target = new CPPClassThatInheritsFromEventTarget();
  const event = new Event('foo');
  const e = await new Promise(resolve => {
    target.addEventListener('foo', resolve, { once: true });
    target.dispatchEvent(event);
  });
  assert(e === event);