Implement minor memory usage optimization for environments without FerriteCore

This is "FerriteCore at home", used to assist with the large registry
tests

Author: embeddedt

common/src/main/java/org/embeddedt/modernfix/common/mixin/perf/mojang_registry_size/StateHolderMixin.java

@@ -0,0 +1,29 @@
+package org.embeddedt.modernfix.common.mixin.perf.mojang_registry_size;
+
+import com.google.common.collect.ImmutableTable;
+import com.google.common.collect.Table;
+import net.minecraft.world.level.block.state.StateHolder;
+import net.minecraft.world.level.block.state.properties.Property;
+import org.embeddedt.modernfix.annotation.RequiresMod;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+/**
+ * Minor mixin to avoid duplicate empty neighbor tables, used when FerriteCore is not present. Won't be enabled in 99% of
+ * modded environments but is useful for testing in dev without dragging in Fabric API.
+ */
+@Mixin(StateHolder.class)
+@RequiresMod("!ferritecore")
+public class StateHolderMixin {
+    @Shadow private Table<Property<?>, Comparable<?>, ?> neighbours;
+
+    /* optimize the case where block has no properties */
+    @Inject(method = "populateNeighbours", at = @At("RETURN"), require = 0)
+    private void replaceEmptyTable(CallbackInfo ci) {
+        if(this.neighbours.isEmpty())
+            this.neighbours = ImmutableTable.of();
+    }
+}