Add 2D triangulation plot

It would be very useful for me adding a new chart type to deal with 2D triangulation (or mesh).

At the current implementation, I found different workarounds but with some limitations:

• the heatmap graph is only for data in grid format
• the mesh3d graph shows three dimensions and it manages also the lights, resulting for my purpose too complex (and expensive)
• the basic scatter plot allows me to draw a single triangle, but if I try for many triangles (>10k) the function is extremely expensive.

I apologize in advance if this feature is already implemented and I missed it.

首先查看现有的 heatmap、mesh3d 和 scatter 图表实现，以了解它们在数据和渲染方面的限制。在提出新的图表类型之前，先定义预期的 2D 三角剖分或网格输入、渲染行为，以及针对大量三角形的性能目标。