Function avg_pool2d_backward 

pub fn avg_pool2d_backward(
    x: Tensor<4>,
    grad: Tensor<4>,
    kernel_size: [usize; 2],
    stride: [usize; 2],
    padding: [usize; 2],
    count_include_pad: bool,
    ceil_mode: bool,
) -> Tensor<4>

Backward pass for the avg pooling 2d operation.