keep cursor position when scrolling

[kirawi]

Discussed in #718

^{Originally posted by sekirocc September 6, 2021}
Hi, when scrolling using C-d C-u, the cursor is now sticking with same line number, which makes the cursor jump back and forth in window.
How about add a config option(or even make it default) to set the cursor stay in same position relative to window.
Just like vim's C-d C-u.

[pascalkuthe]

#7639 was recently created which is about the same thing. That issue has a bunch more discussion (and an example implementation that is pretty good already) so I will close this issue in favour of that