(Stub, we can fill in the details as they become relevant)
The popular ones right now are TypeScript definition files and Closure externs, I believe.
There was some work done a while ago https://github.com/dart-lang/sdk/issues/24874#issuecomment-253935419
Yes, that is a very stale tool. This request is for an updated tool (that is tested on CI, etc).
Are people still interested in such a tool? Workiva is hitting a good deal of pain around JS interop and are considering writing something ourselves.