Add excavator as barge

Sometimes we want to dig rock from the land and create a dock or something. Right now, we can only dig a hole and flood it. We should be able to dig from water for example to -2 below sea

This game is 99% of the time 'soil movement/stacking simulator' so I think controlling soil underwater to an even deeper depth makes sense.

The devs could make a long boom excavator that allows you to dig into the ground deeper and allows you to dig in water up to like 5 tiles deep. It would be a t3 vehicle or even a t4 vehicle and could cost more than the Mega Excavators cost.