Depress/release keys kept down, listed by down_names

Property definitions

gamnit $ RoundControl :: depressed_down
	# Depress/release keys kept down, listed by `down_names`
	private fun depressed_down
	do
		for name in down_names do
			var e = new VirtualGamepadEvent(name)
			e.is_down = false
			app.accept_event e
		end
		down_names.clear
	end
lib/gamnit/virtual_gamepad/virtual_gamepad.nit:273,2--282,4