[drag-drop] cdkDragBoundary positions not updating during viewport scrolling

[Achilles1515]

Reproduction

https://stackblitz.com/edit/angular-v8fc5s

Expected Behavior

cdkDragBoundary should always be honored. The cached boundary positions appear to not be updating during viewport scrolling, producing phantom edges and/or enabling dragging outside of the boundary. See below gif.

Actual Behavior

Environment

• Angular: 9
• CDK/Material: 9.0.1
• Browser(s): all