Spear Skeletons

Allows wither skeletons to pick up spears & use them, in addition to normal melee weapons in vanilla.

Installing on the client fixes the wither skeleton's arm pose, but it will work with vanilla clients.

Note that only some wither skeletons are able to pick up items depending on difficulty. Also, due to vanilla equipping conditions, wither skeletons will only choose enchanted netherite spears over their base stone swords.

Using commands to equip other skeleton variants with spears should also work.

Requested by @it_glaci