Replace the auto-generated Node.js facade with a hand-maintained facade

[armanbilge]

Discussed with @mpilquist today in Discord. The auto-generated Scalably Typed facade has served well, especially during the development of fs2.io.js. However, now that things are stable, the advantages of auto-generation are possibly out-weighed by its downsides:

1. 700+ auto-generated files, of which we use only a small fraction.
2. A Scala.js bundler dependency, which creates 8000 lines of lockfiles and downstream headaches.
   • Automatically commit changes to lockfiles scala-steward-org/scala-steward#2252
3. Maintenance burden:
   • Publishing fs2-node module sometimes fails #2489
   • Remove unused dependency to scalajs-dom #2681
   • Update sbt to 1.6.0 #2775
   • Update sbt-doctest to 0.10.0 #2857
4. Various unsafe casts, due to deficiencies of the underlying Typescript definitions.
5. Not really important, but lack of flexibility to support features like in-memory filesystems etc.

By crafting a minimal, hand-written facade, we can address all of the above and overall reduce the impact of the fs2.io.js cross.

If someone has an appetite to work on this, I'll be thrilled :) otherwise, on my yak-list.