"Raise To/Lower To options or variant for "flatten terrain" brush

Feature added to the terrain tools: a brush to "raise to" and "lower to" for terrain.

Right now, flatten terrain brush will do both at the same time. It lowers terrain higher than it and raises terrain lower than it. But there are times where you have both a wall and a hole side by side, maybe with a small space. These brushes would let you bring the 'floor' of the hole up to the height of the brush with "Raise To" without lowering the wall. And "Lower To" would have the same effect by lowering the wall to the brush without raising sunken terrain up.

Imagine you have a sloped cliff and want to make a ledge jutting out from the side. 'Raise To' would bring the bottom of the cliff up to the ledge's height without lowering the cliff above. Great if you already have things on top!

On the same sloped cliff, you want to widen the walkable path, but you have a river down below with several assets along the banks. 'Lower To' would bring the higher parts of the cliff down, without disrupting the river scene you built below.