[Feature] show tooltip for overlapped point

[purpose233]

What problem does this feature solve?

业务需求： 当气泡的值接近时，气泡会重叠，导致用户查看数据困难，只能通过最顶上的猜其他的值，和用户预期不太一致 期望此时可以同时显示多组值 或 可以在重叠的几组间切换

What does the proposed API look like?

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