Use plotly.min.js in both JS bundles

[nicolaskruchten]

Closes #1873 the opposite way from #1891 so as not to bloat the classic nbextension size. If we wanted to do things the #1891 way we would need to add minification in plotlywidget/webpack.config.js so that the nbextension stays small. I'm indifferent but this way seemed easy :)

This PR also inlines the randstr function the same way, and removes the prepublish: webpack line that fails if webpack isn't globally installed, as well as the nonfunctional build target that calls tsc, replacing them with a build: webpack target that gets called explicitly in the CI step.

The bundle size savings of this change are substantial on a percentage basis: both bundles together are now roughly the size of either bundle, as expected, instead of twice. Also PS I resurrected the jupyterlab-chart-editor and it uses the min bundle right now so the savings should be compounded if all three are installed.

(closes #1891 if merged!)

[nicolaskruchten]

this prepublish thing is deprecated. It seems like NPM tries to run it when doing npm install and fails unless you have webpack installed globally for some reason.

[nicolaskruchten]

this isn't a TypeScript module so this doesn't seem to do much

[nicolaskruchten]

The build for this package is, in fact webpack, and running npm run build does use the installed webpack in node_modules. So now we have to run npm install && npm run build and there are no deprecation warnings :)

[jonmmease]

Did you intend to downgrade plotly.js here?

[nicolaskruchten]

That’s an upgrade actually ;)

[jonmmease]

One question above, but this looks good to me, assuming you've smoke tested the extensions in JupyterLab.

Thanks @nicolaskruchten!

[nicolaskruchten]

I’ve smoke tested by uninstalling, building and reinstalling both extensions... is that about right?