Add StackResolver for backwards compatibility

src/main/java/io/github/thebusybiscuit/slimefun4/api/MinecraftVersion.java

@@ -55,6 +55,12 @@ public enum MinecraftVersion {
      */
     MINECRAFT_1_20_5(20, 5, "1.20.5+"),
 
+    /**
+     * This constant represents Minecraft (Java Edition) Version 1.21
+     * ("Tricky Trials")
+     */
+    MINECRAFT_1_21(21, 0, "1.21+"),
+
     /**
      * This constant represents an exceptional state in which we were unable
      * to identify the Minecraft Version we are using

src/main/java/io/github/thebusybiscuit/slimefun4/utils/multiversion/StackResolver.java

@@ -0,0 +1,31 @@
+package io.github.thebusybiscuit.slimefun4.utils.multiversion;
+
+import io.github.thebusybiscuit.slimefun4.api.MinecraftVersion;
+import io.github.thebusybiscuit.slimefun4.implementation.Slimefun;
+import org.bukkit.Material;
+import org.bukkit.inventory.ItemStack;
+
+/**
+ * This utility class provides backwards compatibility to versions of minecraft
+ * regarding the creation of ItemStacks.
+ *
+ * @author Vaan1310
+ */
+public final class StackResolver {
+
+    private StackResolver() {}
+
+    public static ItemStack of(Material material) {
+        return of(material, 1);
+    }
+
+    public static ItemStack of(Material material, int amount) {
+        var version = Slimefun.getMinecraftVersion();
+
+        if (version.isAtLeast(MinecraftVersion.MINECRAFT_1_21)) {
+            return ItemStack.of(material, amount);
+        } else {
+            return new ItemStack(material, amount);
+        }
+    }
+}