Support loading 1.13+ ItemStacks stored YAML on 1.12.2 and before

[bergerkiller]

BkCommonLib version: 1.15.1-v1-SNAPSHOT

Spigot version: 1.12.2

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Problem or bug:

Loading YAML containing ItemStack information saved on MC 1.13 or later, on MC 1.12.2, does not function in all expected cases

Expected behaviour:

Can load YAML containing itemstacks saved on later versions

Steps to reproduce:

Attempt loading YAML such as:

item:
  ==: org.bukkit.inventory.ItemStack
  type: BIRCH_LEAVES
  meta:
    ==: ItemMeta
    meta-type: UNSPECIFIC
    Unbreakable: true

Which fails to find the material 'BIRCH_LEAVES' (called 'LEAVES' on 1.12.2)

[bbayu123]

Sounds like a pain lol