make mat-step-header header scrollable

#### Please describe the feature you would like to request.
I would like to see the mat-step-header made scrollable in a similar fashion to mat-tab. IOf you have multiple steps on a smaller resolution or inside a container with a specific width the steps simply overflow over the edge and would be better if you have a left/right scroll button on either side of the header like the mat-tab

#### What is the use-case or motivation for this proposal?
I have several apps that use the material stepper (specifically the horizontal stepper) where there are many steps in the flow, the stepper is usually displayed inside a mat-card with a specific width (responsive to difference screen sizes)

On smaller screen sizes where there are more steps than permitted on the screen the step headers simply overflow off the screen

#### Is there anything else we should know?

This is a screen shot of one example on a large mobile (width: 425px)

まず、horizontal mat-step-header の動作とスクロール可能な mat-tab ヘッダーの動作を比較し、狭いコンテナ内で多数の項目をそれぞれどのように処理するかに注目します。モバイルのスクリーンショットで期待される動作を確認し、ステップヘッダーがはみ出さず、使用可能な左右のスクロールコントロールが提供されることを完了条件とします。

索引モデルが issue の本文から書いたものです。