Add support of Trendlines in Charts

[xzxiangzml]

There is no trend line in scatter plot scatter-plot.xlsx

[Rita-Bubnova]

Hello, @xzxiangzml. I can confirm - this is know problem, issue 18064 in our private issue tracker.

[FlyinPancake]

Well this would be a crucial feature for finally ditching office

[jcntrl]

This is a non-starter. Trendlines are simple "must-haves" in any spreadsheeting application, no matter how pretty the application is, otherwise. Even Open/Libre-Office has this functionality.

[G-Boronad]

Please, we really need it for all sciences or économics students...