Optimize ItemBuilder by externalizing ItemMeta

[CosimoTiger]

• initially separate ItemMeta from the ItemStack and store it inside the ItemBuilder instance
• apply it rarely as an optimization measure because the implemented methods in CraftBukkit seem to be expensive (a bunch of checks, instantiations...), and we're constantly getting and setting new copies of ItemMeta
• apply it only in cases when:
  • finalizer build() is called
  • with Consumer method is called, which is when the true current state of the ItemStack needs to be seen and a new ItemMeta may be applied