[CB-6628][amazon-fireos]dialogs plugin's confirm and prompt methods dont work
confirm() method was missing amazon-fireos platform check. added that.
prompt() method had bug. It is executed in a worker thread that does not have a message queue(or Looper object) associated with it and hence "can't create a handler" exception is thrown. To fix this issue, we need to create the EditText widget from within the UI thread. This was fixed sometime ago when we added fireos platform but commit got lost somewhere. So fixing it again now.