src: allow preventing SetPromiseRejectCallback

[codebytere]

This PR slightly augments the existing IsolateSettings struct for embedder purposes.

Electron does not want to use the promise rejection callback that Node.js uses,
because it does not send PromiseRejectionEvents to the global script context in the browser (for fairly obvious reasons).

Therefore, if we want to use Node.js setup logic in the renderer process (as opposed to standalone embedded mode, where we already do this) we would not be able to allow users to do things such as:

window.addEventListener('unhandledrejection', function (event) {
  // ...your code here to handle the unhandled rejection...

  // Prevent the default handling (such as outputting the
  // error to the console)

  event.preventDefault();
});

since the 'unhandledrejection' event would never be fired.

We need to use the one Blink already provides and sets on the Isolate we're given, and so we need to slightly augment IsolateSettings to allow for that.

Checklist

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

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/32366/

[addaleax]

LGTM, but I think it makes sense to use the inverse flag (i.e. SHOULD_NOT_SET_PROMISE_REJECTION_CALLBACK), because then this becomes semver-minor instead :)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/32387/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/32425/