Added dynamic rendering support for the 'label' and 'shadow' properties of the Marker class.

[maslke]

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1. Enhancement of the Marker class functionality by providing toSize and toLabel functions. And it can be dynamically rendering.

  <Marker position={position} label={label} icon={{image: "https://webapi.amap.com/theme/v1.3/markers/0.png", size: [36, 36], imageSize: [36, 36], imageOffset: [0, 0]}} />

3. fix the issue: Marker的label属性中offset不生效 #252