Autocompletion dialog shouldn't push up the input line and previous output

[st0012]

Description

Currently, if autocompletion dialog's height > the remaining space between input line and the terminal bottom, it'll push the input line and previous output up:

This gives a bad user experience because users now need to scroll up to see previous output. In small terminal windows, the frequency to do so is likely very high.

Possible Solution

I think when the space below input line is not enough to display autocompletion dialog, reline should do 2 things:

1. Display the dropdown above the input line instead, which is what VS Code does:

2. If the dialog height still exceeds the available space above, reduce the candidates to make it fit.

Terminal Emulator

This happens in Terminal.app, iTerm2, and Kitty terminal and it's not an emulator-related issue.

[tompng]

I think there are two problems

1. Reline should not corrupt the screen by pushing up (this is a bug of reline). If dialog is too large, reline should not render dialog where it overflows screen.
2. Reline's autocomplete dialog and IRB's document dialog should use an appropriate dialog position and size.

I'll fix problem 1 after #492 is merged. After merged, I think it could be fixed with about +3 lines. (draft pull reques #524)

dialog_pushup_bug.mp4

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[st0012]

@tompng I think we can close this one because of your fixes?