bug(cdkDrag): Issue scrolling/reordering "reversed" lists

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

For design/UX reasons, I'm using `cdk/drag-drop` on a list with `flex-direction: row-reverse` applied. Scrolling does not trigger while dragging among other issues.

Can we get a "reversed" option to support this use case?

### Reproduction

Steps to reproduce:`
1. Apply `display: flex; flex-direction: row-reverse;` to a `cdkDropList`
2. Try to drag+scroll an element

### Expected Behavior

It would be nice if indexes and scroll behavior could work intuitively by adding a `reversed` option

### Actual Behavior

The drag will not scroll the `cdkDropList`

### Environment

- Angular: v19.0.0
- CDK/Material: v19.0.0
- Browser(s): All
- Operating System: Ubuntu

使用列出的复现步骤从 cdkDropList 的拖放行为开始：应用 flex-direction: row-reverse，并在滚动时拖动一个元素。跟踪反向列表中的索引和滚动行为，然后验证在 Angular 19 复现中滚动有效且排序仍然直观。

由索引模型根据 Issue 内容生成。