Cross-publish for Scala.JS?

[alexarchambault]

It seems the classes of scala-async are now required at runtime when using async / await. This breaks Scala.JS projects using scala-async, as it's not cross-published for Scala.JS.

See this test project for a reproduction, or coursier/coursier#1843. The test project README details the linking error one runs into during fastOptJS.

[SethTisue]

In the Scala modules generally, we have gladly merged pull requests adding Scala.js and/or Scala Native cross-builds when they have been submitted by volunteers. (It isn't something we've normally tackled ourselves.)

[OndrejSpanel]

PR submitted.

[SethTisue]

publishing ticket: #276