Add compute_density_function to replace removed `sample_noise (#1591)

src/main/java/carpet/mixins/RandomState_ScarpetMixin.java

@@ -0,0 +1,33 @@
+package carpet.mixins;
+
+import carpet.fakes.RandomStateVisitorAccessor;
+import net.minecraft.world.level.levelgen.DensityFunction;
+import net.minecraft.world.level.levelgen.RandomState;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Unique;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.ModifyArg;
+
+@Mixin(RandomState.class)
+public class RandomState_ScarpetMixin implements RandomStateVisitorAccessor {
+    @Unique
+    private DensityFunction.Visitor visitor;
+
+    @ModifyArg(
+            method = "<init>",
+            at = @At(
+                    value = "INVOKE",
+                    target = "Lnet/minecraft/world/level/levelgen/NoiseRouter;mapAll(Lnet/minecraft/world/level/levelgen/DensityFunction$Visitor;)Lnet/minecraft/world/level/levelgen/NoiseRouter;"
+            ),
+            index = 0
+    )
+    private DensityFunction.Visitor captureVisitor(DensityFunction.Visitor visitor) {
+        this.visitor = visitor;
+        return visitor;
+    }
+
+    @Override
+    public DensityFunction.Visitor getVisitor() {
+        return this.visitor;
+    }
+}