fix: adjust cursor start position for large buffers

[qilme]

nushell/nushell#15436

[fdncred]

Thanks for trying to make nushell and reedline better. Please help me understand how this fixes the issue. If my screen height is 50 how is queuing 50 \n's going to help? Is there a way we can easily try this in the reedline demo to see if it works?

[qilme]

Since reedline uses crossterm and crossterm uses ansi escape sequences to implement the function, I can use nushell to emulate the behavior.

1. scope commands or other command judged as large buffer.If it is a lagre buffer, then prompt_start_row is 0 and nushell send "ESC [0;0H" to terminal.

2. ansi -e "H" is the same as "ESC [0;0H". It clear my viewpoint in the Windows Terminal, vscode, alacritty and termux.

3. Scrool up and content as high as my screen height disappears.

4. scope commands

5. for x in 1..50 { if $x > 30 { break }; print ""}

6. ansi -e "H"

7. Scrool up and content exists

[fdncred]

But don't you have a bunch of empty lines after the buffer?

[qilme]

The demo does have, but the nushell I compiled after patching not.

[qilme]

Origin:

My demo:

My patch: