feat: pie chart add select event

[lxhyl]

Explanation About What Code Achieves:

src/js/charts/PieChart.

add getDataPoint, setCurrentDataPoint, bindUnits methods to getData and set event.

Screenshots/GIFs:

• Screenshot

Steps To Test:

• click pie charts item.
• should trigger the onDataSelect event

TODOs:

• None

  I want to konw is this right? if not. How should i optimize the code.

[uhrjun]

I want to konw is this right? if not. How should i optimize the

No optimization needed. Thanks for making the PR. Simple and concise.