[Feature Suggestion] add way to detect air & non-air above structure jigsaw

This would be useful for something such as remaking mineshafts with jigsaws to allow them to be expanded upon, as doing so would require jigsaws to place chains upwards when there are multiple blocks of air above the mineshaft, whilst still allowing it to check to make sure there is a non-air block at some point above, to ensure the chain does not continue into the sky.