Add Electron start-up performance script

[cdamus]

Feature Description:

An earlier contribution, PR #9777, added a node.js script that measures the start-up time of the browser frontend application, with statistics computed over several runs. The same would be helpful for the Electron deployment.

Because the Electron deployment can behave differently to the Browser deployment, it would be helpful also to enhance the extension-impact.js script to optionally drive the Electron performance measurement script.