PopupMenu scrolling is unusable with keyboard/controller input

[rsubtil]

Godot version

4.2.dev (latest)

System information

Arch Linux

Issue description

Selecting items on PopupMenus by using a keyboard/controller is unusable due to a visual bug. The scrolling position jumps constantly back and forth:

Peek.2023-08-03.15-59.mp4

The selection itself is working properly; only the logic for scrolling to the selected item is wrong. I've bisected it to #57692 (cc @YeldhamDev), and restoring the scroll_to_item code to before this PR fixes the issue:
https://github.com/godotengine/godot/pull/57692/files#diff-7ee2fe488be40211cc85edff72e3668728514546ee530987099f7dc1f057f85cR1294-R1306

Steps to reproduce

• Have an OptionButton with enough options to make it scrollable.
• Attempt to scroll by holding the up/down keys to traverse items.
• Items out of the initial selection will make the scroll position jump back and forth.

Minimal reproduction project

Repro.zip