Adding layoutIterations() support

[qknight]

I'm using the change in this PR already - so it probably can be merged I guess.

If you want to play with it:

https://echarts.apache.org/examples/en/editor.html?c=sankey-simple&lang=ts&version=5.4.4-dev.20231111&decal=1

option = {
  series: {
    type: 'sankey',
    layout: 'none',
    layoutIterations: 0,
    emphasis: {
        focus: 'adjacency'
    },
    data: [
{ name: 'b1' },
{ name: 'b' },
{ name: 'a' },
{ name: 'c' },
{ name: 'a1' },
{ name: 'a3' },
{ name: 'aa' },

    ],
    links: [
      {source: 'b',target: 'b1',value: 1},
      {source: 'a',target: 'a1',value: 5},
      {source: 'a',target: 'b1',value: 2},

      {source: 'b1',target: 'c',value: 2},
      {source: 'b1',target: 'a1',value: 1},
      {source: 'a',target: 'aa',value: 3},
      {source: 'aa',target: 'a3',value: 3},
    ]
  }
};