Text Box Scrolling Issue On Terminal Resize

**Describe the bug**
Expanding the terminal window width causes the text within a scrolled text box to improperly adjust, leading to text disappearing from view instead of reflowing to accommodate the new width.

**To Reproduce**
Steps to reproduce the behaviour:
1. Navigate to any interface element that includes a vertical scrollbar, such as the 'Commit Message Details' window.
2. Decrease the terminal window's width and then scroll to the bottom of the text box.
3. Gradually increase the terminal window's width and observe the behavior of the text within the scrolled text box.
4. Notice that as the window width increases, the text starts to move upwards and eventually goes out of view.

**Expected behavior**
Upon expanding the terminal window's width, the text within a scrolled text box should reflow and adjust accordingly, maintaining the current view position while revealing more text or adjusting the text to fit the new width without losing the current focus point.

**Screenshots**

**Context:**
- OS/Distro + Version: `NixOS 24.05.20240319.b06025f (Uakari)`
- GitUI Version `0.25.1`
- Rust version: `1.75.0`

まず、垂直方向にスクロールしたテキストボックスを使い、報告されている手順に従って Commit Message Details ウィンドウのリサイズ動作を再現します。次に、テキストボックスのリサイズとスクロールの処理を追跡し、ターミナルの幅を広げても現在のフォーカスポイントが維持され、テキストが表示されたままになることを確認します。

索引モデルが issue の本文から書いたものです。