Send user confirmation instead of Terminal Response

On certain proactive commands like  Setup Call/Open Channel,
a confirmation dialog is displayed to the user to confirm or reject the
call. If the user hits the back key to dismiss the dialog or the user
 hits 'No', consider that as the user rejecting the call, instead
of sending a Terminal Response.

Bug: 8302972
Change-Id: I23d57f726018a6805ef455f6069dbab8e6dd14f0