bug(drag-drop): changing the disable state dynamically doesn't work

#### Reproduction

For some reason, in Stackblitz it works: https://stackblitz.com/edit/angular-ghqzcr
But in a new project, the bug also reproduces: https://github.com/doronsever/drag-drop-bug
I copied everything from stackblitz to my project and still doesn't work.

I need the initiate state of the drag and drop to be disabled and only when clicking on the mouse down to enable it.
The reason for that is that I have also a resize option and if the drag and drop is enabled, when resizing it is also dragging the element.

So in my real app, I'm starting with the drag and drop disabled, and on a mousedown event, I check if the mouse is not touching the resize button and only then enabling the drag and drop.
Up until Angular 8, everything worked fine but now that we are trying to upgrade to Angular 9 (and also material to 9, this behavior stopped working).


#### Expected Behavior

When setting the flag to false, enable the dragging even if the mouse is down.

#### Actual Behavior

drag and drop doesn't work

#### Environment

- Angular: 9.1.1
- CDK/Material: 9.2.0
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Mac

まず StackBlitz の再現とリンク先の new-project の再現を比較し、Angular CDK の drag-and-drop セットアップと動的な disabled フラグに注目します。Chrome で Angular 9.1.1/Material 9.2.0 の動作を再現し、その後、mousedown 中にドラッグを有効化できる一方で、リサイズではドラッグが開始されないことを確認します。

索引モデルが issue の本文から書いたものです。