[Feature] Wish word cloud support text as cloud shape

[xuanhun]

What problem does this feature solve?

Wish word cloud support text as cloud shape，like this：

What does the proposed API look like?

add a "shapeType" field to wordCloudChart.wordCloudShapeConfig,

type="text"|"url"|"svg"|"base64"|"shapeName“，

const spec = { type: 'wordCloud', maskShape: '玄', wordCloudShapeConfig:{ shapeType:"text" }, .... }