bug(DragDrop): Drag&Drop not working inside MatDialog and when the page's height is too big

#### Reproduction

Here is a reproduction. There is a button down there which opens a dialog with draggable items.

https://stackblitz.com/edit/angular-9-material-starter-lktwr2?file=src/app/app.component.css

#### Expected Behavior

Drag&Drop should work.

#### Actual Behavior

I have a project where I have a table with a lot of items, and when I scroll down (for example to the middle of the table, page height ~is 4000px), and by clicking on a row I open a dialog where I want to use drag&drop and where it doesn't work (as in the reproduction). But if I click on a row which is at the beginning of the table, drag&drop is working fine.

#### Environment

In the reproduction I used Angular 9, but I see this in Angular 11 as well. Not sure if this fixed in 12th version.

Start with the linked StackBlitz reproduction, especially src/app/app.component.css, and reproduce the drag-and-drop failure inside the dialog after scrolling the page. Compare behavior from the top and middle of the table; done means draggable items work in the MatDialog regardless of page height and the reproduction still behaves correctly in Angular 9 and 11.

Written by the indexing model from the issue text.