[Feature] crosshair's style attribute support function

[xuefei1313]

What problem does this feature solve?

Expect crosshairs to display different colors in different locations

What does the proposed API look like?

crosshair: {
    xField: {
      visible: true,
      line: {
        type: 'line', 
        style: {
          stroke: ()=>{
            return 'blue'
          },
        }
      },
    },
  }