eventSimulation.keyboardTextInput() should not ignore the current text selection

This was not yet implemented due to time constraints:

Openrunner/runner-modules/eventSimulation/lib/content/keyboard.js

Line 131 in a4cab99

// TODO: for now, text is always inserted at the end of the input, ignoring the current selection

However we now encountered a website which requires this feature to properly insert text into a pre-forrmated text input. The text input looks like <input value="__ / __ / ____">, and javascript on the site ensures that the proper characters are replaced when the user inputs a key.