Fix constructor embind

[aminya]

Description of the change

Adds back the removed method from this commit

Fixed Issues

Fixes #11274
Fixes #9704

Allows running Atom's core engine in the browser: atom/superstring#79

Minimal working example

This PR fixes the following
mwe.cpp

#include<emscripten/bind.h>

struct MyStruct {
  bool optionA;
  MyStruct(bool _optionA): optionA{_optionA} {};
};

MyStruct *constructor_(emscripten::val value) {
  bool optionA = false;
  if (value.as<bool>() && value["optionA"].as<bool>()) {
    optionA = true;
  }
  return new MyStruct(optionA);
}

EMSCRIPTEN_BINDINGS(MyStruct) {
  emscripten::class_<MyStruct>("MyStruct")
      .constructor<emscripten::val>(&constructor_);
}

em++ --bind -o mwe.js  -std=c++17  -O0 ./mwe.cpp  --memory-init-file 0

[welcome]

Thank you for submitting a pull request! If this is your first PR, make sure to add yourself to AUTHORS.

[kripken]

cc @wingo @hkleynhans @chadaustin @Brion

[chadaustin]

As long as tests pass, seems okay to me, thanks!

[aminya]

How can I run the embind tests in isolation so I can fix the issue?

[sbc100]

You can run ./tests/runner.py other.test_embind. Or did you mean how can you just run one of the sub-tests within that? If you meant the latter I'm afraid I don't don't.. sadly the embind test is huge and runs a lot of tests within just one.

[stale]

This issue has been automatically marked as stale because there has been no activity in the past year. It will be closed automatically if no further activity occurs in the next 30 days. Feel free to re-open at any time if this issue is still relevant.

[aminya]

I don't understand why the tests failed.