Added Builders.remove_decoratives(shape) to builders.lua

Builders.remove_decoratives(shape) removes any decoratives in the given shape.
Update the map scripts, snakey_swamp and snakier_swamp to use this to remove decoratives from the dividers.

map_gen/maps/snakey_swamp.lua

@@ -39,7 +39,8 @@ local path =
     b.translate(divider, (path_width + divider_width) / 2, path_width / 2),
     b.translate(divider, -(path_width + divider_width) / 2, -path_width / 2)
 }
-path = b.change_tile(path, true, 'water-shallow')
+path = b.change_tile(path, true, 'water-mud')
+path = b.remove_decoratives(path)
 
 -- Water Border
 local water_rectangle = b.rectangle(tile_width, water_height)

map_gen/maps/snakier_swamp.lua

@@ -13,9 +13,9 @@ Event.on_init(
     end
 )
 --input
-local divider_tile = 'water-shallow'
+local divider_tile = 'water-mud'
 local path_width = 30
-local path_length = 100
+local path_length = 120
 local turns = 6 -- must be even; 0 makes a normal ribbon world
 local divider_width = 10
 local water_height = 60 -- setting it to 0 will eliminate the water border; make sure to add another source of water if you do so
@@ -58,6 +58,7 @@ local path = b.any
     }
 
 path = b.change_tile(path, true, divider_tile)
+path = b.remove_decoratives(path)
 
 -- Water Border
 local water_rectangle = b.rectangle(tile_width, water_height)

map_gen/shared/builders.lua

@@ -986,6 +986,22 @@ function Builders.apply_decoratives(shape, decorative_shapes)
     end
 end
 
+--- Removes the decoratives in the given shape
+--- This is useful for example when using shapes of 'water-shallow'
+function Builders.remove_decoratives(shape)
+    return function(x, y, world)
+        local tile = shape(x, y, world)
+
+        if not tile then
+            return false
+        end
+
+        world.surface.destroy_decoratives({position = {x=world.x, y=world.y}})
+
+        return tile
+    end
+end
+
 -- pattern builders
 
 --- Docs: https://github.com/Refactorio/RedMew/wiki/Using-the-Builders#builderssingle_pattern