cdkDrag: with cdkDropList -> wrong Cursor when dragging

Hi all,

**Here is a little sample.**
[https://stackblitz.com/angular/yvmnrxexppp?file=app%2Fcdk-drag-drop-connected-sorting-example.html](url)

Since version 7.2.x (I noticed) there is the problem that the cursor (set in CSS) adapts to the underlying object during the dragging process.

If the cursor is changed to "move" and I use e.g. move an "input" (drag) then the cursor changes from move to input.

This phenomenon only occurs with cdkDropList, not when the cdkDrag property is only set for a single object.

The CSS:
```css
.example-box {
padding: 20px 10px;
border-bottom: solid 1px #ccc;
color: rgba(0, 0, 0, 0.87);

display: flex;
flex-direction: row;
align-items: center;
justify-content: space-between;
box-sizing: border-box;
cursor: move;
background: white;
font-size: 14px;
}
```

The HTML:
```html

Start with the linked StackBlitz reproduction and inspect the cdkDrag and cdkDropList behavior while dragging an input element. Confirm the cursor changes from move to the underlying element's cursor only when cdkDropList is present; done means the drag cursor remains consistent throughout the drag.

Written by the indexing model from the issue text.