feat(build): webpack@5 and webpack-dev-server@4 (#7826)

SwaggerUI is now built using `webpack@5`, with dev support for `webpack-dev-server@4`
- ES Module output bundle path now points to `swagger-ui-es-bundle-core`, which does not include dependencies
- No change to CommonJS output bundle or path
- Now uses Asset Modules, which replaces `file-loader`, `raw-loader`, and `url-loader`
- Removed unused rules/loaders for `.woff | .woff2 | .ttf | .eot` fonts and html
- Node polyfills are no longer bundled with `webpack@5`, and must be loaded separately and/or use `resolve.fallback`. 
As an example, SwaggerUI loads `process`, `buffer`, and `stream-browserify` as `devDependencies` in order to build development and production bundles.

SwaggerUI-React
- Now imports `swagger-ui-es-bundle-core`, and similarly outputs `swagger-ui-es-bundle-core` to its `dist` directory

Dev notes:
- Order of execution matters for the production npm build scripts. `build-stylesheets` needs to get built first, 
then cleanup of any empty artifacts, before building the various production bundles
- `Dev-helpers` now relies on `HTMLWebpackPlugin` to inject css and bundle files

src/core/plugins/all.js

@@ -5,6 +5,8 @@ const request = require.context(".", true, /\.jsx?$/)
 
 const allPlugins = {}
 
+export default allPlugins
+
 request.keys().forEach( function( key ){
   if( key === "./index.js" ) {
     return
@@ -20,5 +22,3 @@ request.keys().forEach( function( key ){
 })
 
 allPlugins.SafeRender = SafeRender
-
-export default allPlugins