build(umd-module): prevent mangling (#4320)

* Prevent mangling of names in UMD distribution

This makes debugging easier in general.

* use `uglifyOptions`

webpack-dist-standalone.config.js

@@ -20,6 +20,7 @@ module.exports = require("./make-webpack-config.js")(rules, {
   _special: {
     separateStylesheets: true,
     minimize: true,
+    mangle: true,
     sourcemaps: true,
   },