Upgrade to Webpack 5

[davidwatkins73]

• [x] Upgrade core webpack
• [x] Update webpack.config.js (and dev/prod)
  • [x] convert contentBase to static
  • [x] remove file-loader, replacing with built-in type: "asset/resource" declaration
• [ ] Test on IE
• [ ] understand implication of removing disableHostCheck in dev webpack config
• [ ] understand why a name is needed in the optimization\split-chunks comm webpack config

[davidwatkins73]

REsulting build had problems on IE. Not sure if this was Svelte or Webpack.