All cdkDrag items in a CdkDrop element are assumed to be members of a reorderable list

Currently all `cdkDrag` items in a `CdkDrop` element are treated as reorderable items in a list. While the underlying data structure is still left to the developer, the `CdkDragDrop` system updates the UI temporarily with changes to the "list order" even if the items are not supposed to be treated as a list.

Instead, we should have two directives for `CdkDrop` areas, `cdkDropZone` and `cdkDropList`. The former, does not do any automatic UI changes during the drag action and the latter does the current action of reordering items in the list.

Comienza rastreando los puntos de entrada CdkDrop, CdkDragDrop, cdkDropZone y cdkDropList descritos en el issue. Determina cómo el comportamiento actual de drop actualiza el orden de la lista y, a continuación, define los comportamientos separados de modo que cdkDropZone deje sin cambios el orden de la UI, mientras que cdkDropList conserve el reordenamiento.

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