reactivate terser compress and mangle

thanks to the new es6 exports defined in the index.ts, terser is able to
generate a minified bundle including right export names.

The minified bundle size decreases from 180.99 kb to 129.64 kb.

export{or as BpmnVisualization,lr as DropFileUserInterface,I as IconPainter,O as
IconPainterProvider,i as MarkerIdentifier,N as StyleConfigurator,s as
StyleDefault,a as StyleIdentifier,x as buildPaintParameter,y as
computeScaledIconSize,ir as documentReady,dr as handleFileSelect,ur as loadBpmn,
sr as log,ar as logStartup,pr as readAndLoadFile};

rollup.config.js

@@ -80,8 +80,6 @@ if (devMode) {
 if (demoMode) {
   plugins.push(
     terser({
-      compress: false,
-      mangle: false,
       ecma: 6,
     }),
   );