feat(LuaEngine/Packed GUIDs) Add support for writing packed GUIDs and reading packed GUID size

[mostlynick3]

This lets users create and manipulate packets that involve packed GUIDs as opposed to full GUIDs directly.

Example implementation, where the client needs to receive a packed GUID:

local function OnCommand_TestPackedGUID(event, player, command)
    if not (command == "testPackedGUID") then return end

    local SMSG_FORCE_MOVE_ROOT = 0x0E8

    local playerGuid = player:GetGUID()
    local packedSize = GetPackedGUIDSize(playerGuid)
    local PACKET_SIZE = math.min(packedSize + 4, 13)  -- Ulong is 4 bytes, packed GUID is up to 9 bytes

    local packet = CreatePacket(SMSG_FORCE_MOVE_ROOT, PACKET_SIZE)
    packet:WritePackedGUID(playerGuid)
    packet:WriteULong(2)

    player:SendPacket(packet)
    player:SendBroadcastMessage("You have been rooted by a packet and your packedGUID!")
    return false
end

RegisterPlayerEvent(42, OnCommand_TestPackedGUID)