bug(cdkDrag): Items in DropLIst Jump Down When Using DragBoundary or ConstrainPosition with Custom Preview

### 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

Items with a custom preview inside of a drop list that should be constrained either by constrainPosition or a dragBoundary appear to jump down for one frame when being dragged before constraint is applied.

### Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-eyxb1gn5?file=src%2Fmain.ts

### Expected Behavior

Constraints are applied to drag preview on starting frame of drag.

### Actual Behavior

Constraints are not applied to drag preview until the second frame of the dragging.

### Environment

- Angular: 19.0.6
- CDK/Material: 19.1.2
- Browser(s): Chrome/Firefox
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

Start with the linked StackBlitz reproduction and its src/main.ts entry point, then reproduce the drag behavior with a custom preview and either dragBoundary or constrainPosition in Chrome or Firefox. Done means the drag preview has its constraint applied on the starting frame, without a one-frame downward jump.

Written by the indexing model from the issue text.