codegen: Add valid support for const multi-dimensional arrays

For example this
  const int[,,] tri_numbers = {{{1, 2, 3}, {5, 5, 6}}, {{6, 7}}};
correctly transfoms to
  const gint tri_numbers[2][2][3] = {{{1, 2, 3}, {5, 5, 6}}, {{6, 7}}};

https://bugzilla.gnome.org/show_bug.cgi?id=604371