Fix Buffer creation from Lua

[jadarve]

The script below does not work:

local builder = ll.class(ll.ComputeNodeBuilder)

function builder.newDescriptor() 
    
    local desc = ll.ComputeNodeDescriptor.new()
    
    desc.builderName  = 'Square'
    desc.localShape   = ll.vec3ui.new(32, 1, 1)
    desc.gridShape    = ll.vec3ui.new(1, 1, 1)
    desc.program      = ll.getProgram('Square')
    desc.functionName = 'main'

    desc:addPort(ll.PortDescriptor.new(0, 'in_buffer', ll.PortDirection.In, ll.PortType.Buffer))
    desc:addPort(ll.PortDescriptor.new(1, 'out_buffer', ll.PortDirection.Out, ll.PortType.Buffer))

    return desc
end

function builder.onNodeInit(node)
    
    local in_buffer = node:getPort('in_buffer')

    -- Allocate out_buffer in the same Memory as in_buffer
    local memory = in_buffer.memory
    
    -- TODO: call createBuffer using default usage flags
    -- TODO: overload of createBuffer with in_buffer.usageFlags does not work. Need unsafe version
    local out_buffer = memory:createBuffer(in_buffer.size)
    
    -- bind the output
    node:bind('out_buffer', out_buffer)
    
    -- configure the dispath shapes according to the size of in_buffer
    node:configureGridShape(ll.vec3ui.new(in_buffer.size / 4, 1, 1))

end

ll.registerNodeBuilder('Square', builder)