Closing a pane does not reset the PowerShell text position

[richardszalay]

Environment

Windows build number: Microsoft Windows [Version 10.0.18362.175]
Windows Terminal version (if applicable): 0.3.2171.0

Steps to reproduce

1. Create a PowerShell tab
2. Press enter until the text covers most of the window
3. Split the view horizontally
4. Close the bottom pane
5. Start typing

Expected behavior

Text appears at previous cursor line

Actual behavior

Text appears in blank space. Screenshots of process:

[zadjii-msft]

So this is definitely a psreadline bug, though it does seem unique to Windows Terminal. Notably, I can't seem to repro a similar scenario in a conhost window:

1. Do a wsl.exe powershell.exe to get a conpty running powershell in a conhost window.
2. fill the buffer
3. Resize down so the prompt is in the middle of the buffer
4. Resize up again
5. type anything

If this was a purely psreadline or conpty bug, then this wouldn't repro in this scenario. We'll need to do something better with the Terminal specifically.

[DHowett-MSFT]

This is partially related to the fact that PowerShell saves and restores your cursor position across taking prompt input. That's also the cause of #2267.