[Webpack 5.x] Upgrade examples + demos to webpack 5.x

[mdhsl]

[mdhsl]

After getting issue while compiling Cesium 1.85.x using Webpack 4.x, it seems that using webpack 5.x fixes the issue.

Anyway, in a continuous evolutionary logic of the Toolkit, it is interesting to upgrade the versions of the libs when we need them.

We have also to upgrade/update:

• upgrade webpack, webpack-cli to 5.x and all associated plugins to last version
• Update copy plugin setup (has been changed)
• Remove options from worker-loader plugin (see https://webpack.js.org/guides/web-workers/#root)
• Update showcase
• Update demos
• Replace node: { fs: 'empty' } by

resolve: {
    fallback : {
      "path": require.resolve("path-browserify"),
      "crypto": false,
      fs: false
    }
}