Optimize "vivliostyle.min.js" built from TypeScript source

[MurakamiShinyu]

With the default settings of webpack.config.js, object property names (including class method names) are not mangled and long names remain.

This can be changed with the Mangle properties options in the webpack.config.js.

Proposed setting:

const TerserPlugin = require("terser-webpack-plugin");
...
module.exports = {
  ...
  optimization: {
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          mangle: {
            properties: {
              keep_quoted: true,
              regex: /^[a-z]{2,}[A-Z]\w*$/,
              reserved: [
                "docTitle",
                "getCurrentPageProgression",
                "getPageSizes",
                "isTOCVisible",
                "layoutStyle",
                "loadDocument",
                "loadPublication",
                "loadXML",
                "navigateToInternalUrl",
                "navigateToPage",
                "printTimings",
                "queryZoomFactor",
                "setOptions",
                "showTOC"
              ]
            }
          }
        }
      })
    ]
  }
};

In this setting, property names to be mangled are limited to camelCase names starting with at least two lowercase letters and contains at least one uppercase letter. Most such names can be mangled safely, but there are some camelCase property names that need to be accessed with that name, listed in the reserved array.

[MurakamiShinyu]

Done. Further improvements will be made later.