`forEachChild` is hard to use with async API

If you try to use the async API, it's a challenge today. The API provides a synchronous tree traversal function (forEachChild), but pulling on semantic information is asynchronous.

The problem isn't the mixture itself - it's that forEachChild stops walking when the visitor function returns a truthy result. This makes it impractical to use with async APIs because every async function returns a Promise which is truthy.

The current workarounds are a little awkward, basically introducing a layer of indirection between the traversal function and forEachChild that uses intermediate queues.

I'm not sure if there's an ideal solution - there's at least two problems right now:

• it feels like we could benefit from a forEachChildAsync or something like that.
• using forEachChild is a foot-gun if you've decided to use the async API.