CircleCI: use scripts for javascript build

[dan-rigdon-bel]

As of #189, we can now use:
script/boostrap.py --platform js (optional)
followed by:
script/setup.py --platform js --overwrite
followed by:
script/build.py --platform js --overwrite --verbose

This is (🤞) a more robust version of of src/build_javascript.py.

Once this is done, I believe src/build_javascript.py can be deleted.

Documentation is updated here:
https://github.com/mcneel/rhino3dm/blob/master/docs/javascript/RHINO3DM-BUILD.JS.md

I have only tested these scripts on macOS. If there are problems on linux, please let me know.

[mcneel-build]

Linked with RH3DM-73

[fraguada]

UPDATE 2021.05.20: Circle CI still uses src/build_javascript.py while the build instructions use bootstrap, setup, build.py

[pearswj]

I didn't do a good job of documenting why I didn't yet adopt the build scripts for the CI build, but #278 sounds familiar. Anyway, we ought to move to GitHub Actions to make it easier for other in the team to help maintain the builds (#373).