array(2) {
  [0] => array(3) {
    [0] => string(3) "16G"
    [1] => string(3) "32G"
    [2] => string(3) "64G"
  }
  [1] => array(2) {
    [0] => string(1) "L"
    [1] => string(2) "XL"
  }
}

计算所有组合
['16G','L']
['16G','XL']
['32G','L']
['32G','XL']
['64G','L']
['64G','XL']
应该怎么组合成这样的结果
array(6) {
  [0] => array(3) {
    [0] => string(3) "16G"
    [1] => string(3) "L"
  }
  [1] => array(3) {
    [0] => string(3) "16G"
    [1] => string(3) "XL"
  }
  [2] => array(3) {
    [0] => string(3) "32G"
    [1] => string(3) "L"
  }
  [3] => array(3) {
    [0] => string(3) "32G"
    [1] => string(3) "XL"
  }
  [4] => array(3) {
    [0] => string(3) "64G"
    [1] => string(3) "L"
  }
  [5] => array(3) {
    [0] => string(3) "64G"
    [1] => string(3) "XL"
  }
 }