Pass letter selected to the keyboard.textChangedCallback function

Tips on how to write a feature request:

  1. Describe your reason for requesting this feature. What problems are you running into?

Currently to determine what letter or action as pressed you need to analysis keyboard.text which is kinda a pain.

  1. How would this request improve your experience developing for Playdate?

Make it easier to create actions specific to certain letters being inputted.

  1. Include any other details you have relating to this request.