Quick diff peek widget ignores editor.scrollbar.verticalScrollbarSize/horizontalScrollbarSize

The gutter "quick diff" peek widget (the small inline diff popup shown when clicking the colored change indicator bar next to line numbers for uncommitted changes) hardcodes its scrollbar size instead of honoring the user's `editor.scrollbar.verticalScrollbarSize` / `editor.scrollbar.horizontalScrollbarSize` settings.

## Steps to Reproduce

1. Set the following in `settings.json`:
```json
"editor.scrollbar.verticalScrollbarSize": 6,
"editor.scrollbar.horizontalScrollbarSize": 6
```
2. Reload the window.
3. Edit a tracked file and make an uncommitted change.
4. Click the colored change indicator bar in the gutter to open the inline "Open Changes" quick diff peek popup.

## Expected

The peek widget's scrollbar should respect the same `editor.scrollbar.*` settings used by the regular editor and the full diff editor tab.

## Actual

The peek widget's scrollbar stays at the default size regardless of user settings, because the size is hardcoded in the widget's editor options rather than read from configuration:

```js
scrollbar: {
verticalScrollbarSize: 14,
horizontal: "auto",
useShadows: true,
verticalHasArrows: false,
horizontalHasArrows: false
}
```

(seen in `workbench.desktop.main.js`, in the quick-diff peek widget's `_fillBody` method that constructs the embedded `diffEditor` instance)

## Request

Please make the quick diff peek widget's scrollbar size configurable / inherit from `editor.scrollbar.verticalScrollbarSize` and `editor.scrollbar.horizontalScrollbarSize`, consistent with the regular editor and full diff editor.

## Environment

- VS Code: 1.129.1 (commit 8a7abeba6e03ea3af87bfbce9a1b7e48fed567b8), arm64
- OS: macOS