When working with a viewport you should call Viewport.input() to pass
the input, but if the input was unhandled you might also want to call
Viewport.unhandled_input() so that objects in the sub-scene can handle
the event. This adds a way to check if the input was handled so that you
know whether you should call Viewport.unhandled_input() or not.
Signed-off-by: Saggi Mizrahi <saggi@mizrahi.cc>
245ace6e2e