Add ItemStack#displayName to get the formatted display name of an ItemStack (#5628)

The display name includes formatting such as item hover event, display name (in italics if renamed in anvil), and color based on rarity.

This is what vanilla uses for give command feedback, and when an item is shown in a death message.

Spigot-Server-Patches/Implement-ensureServerConversions-API.patch

@@ -11,8 +11,8 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 --- a/src/main/java/org/bukkit/craftbukkit/inventory/CraftItemFactory.java
 +++ b/src/main/java/org/bukkit/craftbukkit/inventory/CraftItemFactory.java
 @@ -0,0 +0,0 @@ public final class CraftItemFactory implements ItemFactory {
-         final net.minecraft.nbt.NBTTagCompound tag = CraftItemStack.asNMSCopy(item).getTag();
-         return net.kyori.adventure.text.event.HoverEvent.showItem(op.apply(net.kyori.adventure.text.event.HoverEvent.ShowItem.of(item.getType().getKey(), item.getAmount(), io.papermc.paper.adventure.PaperAdventure.asBinaryTagHolder(tag))));
+     public net.kyori.adventure.text.@org.jetbrains.annotations.NotNull Component displayName(@org.jetbrains.annotations.NotNull ItemStack itemStack) {
+         return io.papermc.paper.adventure.PaperAdventure.asAdventure(CraftItemStack.asNMSCopy(itemStack).displayName());
      }
 +
 +    // Paper start