Webpack 4 example

[jjspace]

This PR adds a separate example for Webpack version 4 alongside Webpack 5. Ideally most people should be on version 5 as soon as possible and on all new products. However, older projects or ones using older versions of frameworks like Nuxt2 and older Angular versions still rely on Webpack version 4

There are some challenges wrapped in getting this to work for Webpack 4 which mostly stem from using newer JS features that Webpack doesn't know how to support.

• Requires babel for transformations like optional chaining (.?)
• Requires a new loader to let Webpack understand import.meta (@open-wc/webpack-import-meta-loader)
  • This seems not ideal and definitely seems to increase build time, may want to look into an alternative
• Requires ignoring "critical" errors about not being able to fully statically analyze cesium's code
  • Speaking with @ggetz this is unavoidable with the way cesium needs to be structured. However Webpack 5 doesn't require any extra config for this which is very curious to me

I also updated the github actions to make sure to perform the build checks and linting against both webpack 4 and 5 versions.

Testing

• Change to both the webpack-4 and webpack-5 directories
• Run npm install
• Run npm run build
• Run npm start and make sure the page works correctly at http://localhost:8080/
• Run npm run start:built and make sure the page works correctly at http://localhost:8080/

There should not be any errors in the console or on the page for both version 4 and 5

[jjspace]

@ggetz I wasn't totally sure the best place to do linting so right now it's in each directory as a "complete package" but it may make more sense to still initialize the whole project as a npm project and do it only at the top level? I haven't worked with npm workspaces or anything but would that make more sense here?

I also realized that this method may not work with husky? Thoughts?

[jjspace]

@ggetz I restructured the packages a little pulling eslint, prettier and husky up to the top level as discussed this morning. I tried using the npm workspaces but realized that it's optimizations for package install locations make the examples trickier, specifically the "copy static files" step. I decided to not use workspaces in favor of having each example stand on it's own and work in isolation to allow people to copy it into their own project easier.

[jjspace]

Thanks for the comments @ggetz, I've addressed or responded to them all, please take another look

[jjspace]

@ggetz updated again, I reorganized the main readme to avoid confusion

[ggetz]

Awesome. Thanks @jjspace!