Is there a tool to view a whole Minecraft world as a map?

uNmINeD. Point it at your save folder and it renders the whole explored world as a zoomable map, with a 3D mode if you want it. It's what everyone uses for this. If you want to see unexplored terrain too, Chunkbase does it from the seed instead of the save, but that's a prediction rather than what's actually generated. For big worlds expect the first render to take a while.