Drag Drop: mat-grid-tile does not retain height when being dragged

#### What is the expected behavior?
When dragging an item in a list, element rendered next to the user's cursor should look exactly like the element that is being dragged.

#### What is the current behavior?
Height changes and becomes bigger when item is being dragged

#### What are the steps to reproduce?
I use Mat-Grid-List example available in the docs at https://stackblitz.com/angular/oegmxkolgyr?file=app%2Fgrid-list-overview-example.html

Just display it on one line because of "Drag Drop Sortable, mixed orientation support (#13372 )" bug and add drag/drop like this:

```

1
2
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4

```


When rowHeight is set to a ratio, height of item being drag changes.

Any solution to keep height at correct ratio?

まず、mat-grid-list マークアップと比率ベースの rowHeight を使って、リンク先の StackBlitz で問題を再現します。ドラッグプレビュー中の mat-grid-tile と drag/drop の相互作用を調査します。ドラッグされたタイルが元のタイルと同じ高さと幅の比率を維持すれば完了です。

索引モデルが issue の本文から書いたものです。