cdkDrag override transform styles

#### Bug, feature request, or proposal:
Bug

#### What is the expected behavior?
When I have transform style on my draggable element, after dragging the transform style will remain.

#### What is the current behavior?
When I have transform style on my draggable element, after start dragging the transform style is overridden.

#### What are the steps to reproduce?
For example add `transform: rotate(45deg);` to `.example-box` here:
https://stackblitz.com/angular/lkdvnnkjmlq?file=src%2Fapp%2Fcdk-drag-drop-overview-example.css
You can notice that after dragging the rotate will disappear.
But, if you will add the `transform: rotate(45deg);` in `style` attribute you will see that the expected behavior is achieved.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
@angular/cdk/drag-drop 8.2.3

Start with the linked StackBlitz reproduction and inspect the Angular CDK drag-drop handling for the .example-box transform. Confirm that a stylesheet transform such as rotate(45deg) remains after dragging, while preserving the behavior demonstrated by the inline style example.

Written by the indexing model from the issue text.