Initial bushes: apple, acacia.

Add 2 "bushes" schematics and plant them through mapgen.

These bushes are not growable through saplings. Only mapgen places
them.

The apple bush is planted in jungles and forms an underbrush that makes
traversing the jungle less appealing, but not by much.  I've chosen
to keep the cover relatively sparse, so that plenty of jungle grass
can still be found.

In grassland we plant them differently, with a sparse noise param. It
creates the much needed bushes in these often large biomes, but
they're still rare enough to require a modest walk.

The acacia bush is a simple 3x3 bush, and planted sparsely like
logs. It's sparse enough to make a nice addition.

mods/default/mapgen.lua

@@ -984,7 +984,7 @@ end
 function default.register_decorations()
 	minetest.clear_registered_decorations()
 
-	-- Apple tree and log
+	-- Apple tree and log and bush
 
 	minetest.register_decoration({
 		deco_type = "schematic",
@@ -1038,6 +1038,37 @@ function default.register_decorations()
 		rotation = "random",
 	})
 
+	minetest.register_decoration({
+		deco_type = "schematic",
+		place_on = {"default:dirt_with_grass"},
+		sidelen = 80,
+		fill_ratio = 0.02,
+		biomes = {"rainforest"},
+		y_min = 1,
+		y_max = 31000,
+		schematic = minetest.get_modpath("default").."/schematics/apple_bush.mts",
+		flags = "place_center_x, place_center_z",
+	})
+
+	-- noise-based bushes in sandstone grassland
+	minetest.register_decoration({
+		deco_type = "schematic",
+		place_on = {"default:dirt_with_grass"},
+		sidelen = 16,
+		noise_params = {
+			offset = -0.05,
+			scale = 0.1,
+			spread = {x = 200, y = 200, z = 200},
+			seed = 2,
+			octaves = 3,
+			persist = 0.66
+		},
+		biomes = {"stone_grassland", "sandstone_grassland"},
+		y_min = 1,
+		y_max = 31000,
+		schematic = minetest.get_modpath("default").."/schematics/apple_bush.mts",
+		flags = "place_center_x, place_center_z",
+	})
 	-- Jungle tree and log
 
 	minetest.register_decoration({
@@ -1133,7 +1164,7 @@ function default.register_decorations()
 		rotation = "random",
 	})
 
-	-- Acacia tree and log
+	-- Acacia tree and log and bush
 
 	minetest.register_decoration({
 		deco_type = "schematic",
@@ -1185,6 +1216,25 @@ function default.register_decorations()
 		rotation = "random",
 	})
 
+	minetest.register_decoration({
+		deco_type = "schematic",
+		place_on = {"default:dirt_with_dry_grass"},
+		sidelen = 16,
+		noise_params = {
+			offset = 0,
+			scale = 0.002,
+			spread = {x = 200, y = 200, z = 200},
+			seed = 2,
+			octaves = 3,
+			persist = 0.66
+		},
+		biomes = {"savanna"},
+		y_min = 1,
+		y_max = 31000,
+		schematic = minetest.get_modpath("default").."/schematics/acacia_bush.mts",
+		flags = "place_center_x, place_center_z",
+		rotation = "random",
+	})
 	-- Aspen tree and log
 
 	minetest.register_decoration({