feat(menu): Add delay before closing nested menu after mouse leave

### Feature Description

**Problem**

When navigating through nested menu items, we must follow a tight path, otherwise it'll close the nested menu.

**Proposed Solution**

In the current behavior, after the mouse leave, the menu is closed.
If we add some delay, before closing the nested menu after the mouse leave event, we could leverage from better navigation.

**Sugestion**

Add an option (matMenuNestedCloseDelay) to change the behavior of closing the nested menu.
When this option is used, it should wait X miliseconds (similar to matTooltipShowDelay) before closing the nested menu after mouse leave.

Also add this option to [MatMenuDefaultOptions](https://material.angular.io/components/menu/api#MatMenuDefaultOptions) to allow override this behavior with injection token.

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### Use Case

If I try to selected the 90 days options, througth the smallest path, it closes the nested menu.


**Desired Behavior**

Taken from [stackoverflow](https://stackoverflow.com/a/50953452) with similar issue.

まず、ネストされた mat-menu でマウスが離れたときに閉じる挙動を追跡し、要求された遅延を matTooltipShowDelay と比較します。matMenuNestedCloseDelay を mat-menu と MatMenuDefaultOptions でどのように公開するかを定義し、メニューの既存のテストで遅延クローズの挙動と injection-token のオーバーライドを検証します。

索引モデルが issue の本文から書いたものです。