Expose /pure build that doesnt depend on OS or require

[Andarist]

This is just a proof of concept - I would gladly work on this to move it through the finish line. However, those kinds of changes might really depend on personal preferences etc so I might need some guidance and code review to do that.

Why?
I'm using a Babel parser and I don't want to pull in a dependency like esprima if I don't have to.

How?

• created a new /pure entrypoint. The name is questionable and I'm happy to change it - I've just wanted this to be terse and couldn't figure out a better one on the spot
• I've removed deprecated esprima option
• I've also removed dual @babel/parser/babylon loading
• and I've removed the dependency on require("os").EOL. I can bring it back in a similar fashion - by splitting the pure and impure files and only using this in the "impure" one