cdkDropList events not triggered within a mat-table row

#### What is the expected behavior?
When the table row is set to cdkDropList it should treat cdkDrag items within the row as list items, reordering where necessary and triggering cdkDropListDropped on release

#### What is the current behavior?
mat-header-cells with the cdkDrag property inside a cdkDropList mat-header-row are behaving as if they are normal cdkDrag items without a cdkDropList.

#### What are the steps to reproduce?
https://stackblitz.com/edit/angular-3x3fbt

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
9.1.3

#### Is there anything else we should know?
Similar issue: https://github.com/angular/components/issues/13770

Comienza con la reproducción vinculada en StackBlitz e inspecciona cómo interactúan cdkDropList y cdkDrag dentro de una fila de encabezado de mat-table. Compara el comportamiento con el issue similar #13770 y verifica si la fila trata los arrastres de mat-header-cell como elementos de la lista. Se considera terminado cuando la reordenación funciona y cdkDropListDropped se dispara al soltar.

Escrito por el modelo de indexación a partir del texto del issue.