src: expose Environment::kNodeContextTagPtr

[codebytere]

This PR exposes Environment::kNodeContextTagPtr. This was introduced a while back in #19134, and then recently introduced into Environment::GetCurrent.

Electron uses Environment::GetCurrent in several places (such as here), and since kNodeContextTagPtr wasn't exposed, we began to run into undefined symbol errors.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

[nodejs-github-bot]

@codebytere build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/1251/pipeline

[addaleax]

Uh … this is implementation details and I’d really like to avoid exposing it.

Environment::GetCurrent() isn’t public API either, fwiw.

How about exposing a public wrapper for Environment::GetCurrent() instead?

[addaleax]

@codebytere Would you like to implement the suggestion above? I think it could be something like a Environment* GetNodeEnvironment(v8::Local<v8::Context>) function, maybe near GetCurrentEventLoop() in the hearders/source code?