editMeta: tighten contract via docs (#5714)

Spigot-API-Patches/0307-ItemStack-editMeta.patch

@@ -5,16 +5,23 @@ Subject: [PATCH] ItemStack#editMeta
 
 
 diff --git a/src/main/java/org/bukkit/inventory/ItemStack.java b/src/main/java/org/bukkit/inventory/ItemStack.java
-index 1bd9f7582bb907ff178fd110fdc92834885d1d78..3e2c08641edffcf00b230ad624685aaff30af0e5 100644
+index 1bd9f7582bb907ff178fd110fdc92834885d1d78..a7909406e9d54c1ab4789b984ed6b1da50837fce 100644
 --- a/src/main/java/org/bukkit/inventory/ItemStack.java
 +++ b/src/main/java/org/bukkit/inventory/ItemStack.java
-@@ -542,6 +542,24 @@ public class ItemStack implements Cloneable, ConfigurationSerializable, net.kyor
+@@ -542,6 +542,31 @@ public class ItemStack implements Cloneable, ConfigurationSerializable, net.kyor
          return result.ensureServerConversions(); // Paper
      }
  
 +    // Paper start
 +    /**
 +     * Edits the {@link ItemMeta} of this stack.
++     * <p>
++     * The {@link java.util.function.Consumer} must only interact
++     * with this stack's {@link ItemMeta} through the provided {@link ItemMeta} instance.
++     * Calling this method or any other meta-related method of the {@link ItemStack} class
++     * (such as {@link #getItemMeta()}, {@link #addItemFlags(ItemFlag...)}, {@link #lore()}, etc.)
++     * from inside the consumer is disallowed and will produce undefined results or exceptions.
++     * </p>
 +     *
 +     * @param consumer the meta consumer
 +     * @return {@code true} if the edit was successful, {@code false} otherwise