[List] support "expand and collapse" from List spec

#### Please describe the feature you would like to request.
The [List spec](https://material.io/design/components/lists.html#types) includes an "Expand and collapse" control. This functions more or less like an Expansion Panel but with List Item styling: dividers are used instead of a surrounding border / different background color, and the expand/collapse button is placed according to the rules for secondary action buttons.

#### What is the use-case or motivation for this proposal?
Support full capabilities of List as described in the spec

#### Is there anything else we should know?
I put together [a StackBlitz](https://stackblitz.com/edit/angular-material2-issue-list-expand) showing the current behavior when an expansion panel is placed in a list. The behavior is more or less as expected but the styling does not work as a list item, and just "fixing up" the current behavior is a lot to ask of consumers.

In my own project I built a component to implement this behavior, but it's not going to be as robust as it would be if supported directly here. Of course, styling an expansion panel to behave correctly when used as a list item is only one approach, and I don't mean to suggest a specific design. My custom component tracks its own expansion state and handles divider logic, etc, internally.

リンクされている StackBlitz から始めて現在の動作を再現し、その後、既存の List コンポーネントと Expansion Panel コンポーネントをリンクされている List の仕様と比較します。展開/折りたたみの動作、区切り線、リスト項目のスタイリング、セカンダリアクションボタンの配置が要求されたデザインと一致すれば作業は完了です。payload には特定のファイルやテストは記載されていません。

索引モデルが issue の本文から書いたものです。