[Feature] displaying a heatmap on a map within polygons, similar to a height level map

### What problem does this feature solve?

Is there a way to display points as a heatmap on the world map, but not on top of the geoJSON map, as in the example on [heatmap-bmap example](https://echarts.apache.org/examples/en/editor.html?c=heatmap-bmap), but to draw them on the surface of the earth (map polygons) so that the radius and blur do not go beyond the boundaries of the territory. That is, like a height map, perhaps there are already examples with a height map in echarts? It would be great if someone could share or advise how to do this

### What does the proposed API look like?

Perhaps it would be possible to draw directly on polygons in renderItem? I'm not very familiar with the API yet