[Maps] Add water level support to Flood
In addition to the existing "Shallow" water level two water levels are added:
- Deep: Only ships can reach other islands
- Rising: The water level changes from Shallow to Deep to a level where the home islands are flooded.
Accepted By: @real_tabasco_sauce
Comments By: @marder, @vladislavbelov
Differential Revision: https://code.wildfiregames.com/D5139