Elevation: Set Max Height/Max depth

Being able to control the maximum height and maximum depth using the terrain tool would be a significant QoL improvement to better control elevation changes on a map.

Creating elevation changes using rooms (without walls and floors, etc.) gives that level of control (make a ravine exactly -1.5, and hills exactly 2.3, then smooth and adjust everything down from there), but this creates blocky, inorganic-looking elevation changes.