* terminal: add prompt when breakpoint is hit during next/step/stepout
Adds a prompt asking the user what to do when a breakpoint is hit on a
different goroutine while next/step/stepout is being executed.
Gives the user the opportunity to cancel next/step/stepout, continue
once skipping the breakpoint or automatically skipping all other
concurrent breakpoints until next/step/stepout is finished.
Fixes#2317