feat(mat-menu): Open nested menus should be delayed on hover.

### Feature Description

An option to delay the menu of nested items would be great.
This prevents the menus from blinking/flashing when you just hover/move the mouse quickly to another wanted item.

Solution: Add delay before opening the nested menu. Only a few milliseconds to prevent flashing menus when you just move the mouse around. The user can still click on a nested item to trigger the menu instantly. This will improve the UX. It's really annoying if the menus are flashing.

You can test my suggested behavior in other proven menus like in Windows 10. Just open a folder and open the context menu. You'll see that the nested menus don't open immediately. They are delayed. Same behavior in VSCode. A shorter delay than the Windows menus, but they are delayed. And I think we should implement this for the mat-menus too.

|mat-menu| vs-code |
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https://material.angular.io/components/menu/examples

Summary:
- Delay nested menu on hover.
- Open nested menu instantly on click.
- Delay nested menu before close (hover leave).
- Implement it with fixed delay time or as an option property with default value (the time in ms. Not just boolean).

Btw: Another related issue which is about delay before closing: #24476
We could combine both issues to add delay before and after.

I think this issue is more a bug than a feature. An unwanted behavior / bad UX. But anyway, it's no candidate for votes. It something what should be considered by the Angular team.

Inizia con l’implementazione di mat-menu e il problema correlato del ritardo nella chiusura #24476, quindi confronta il comportamento richiesto con gli esempi di menu Material collegati. Il lavoro è completato quando i menu annidati si aprono dopo un breve ritardo al passaggio del mouse, si aprono immediatamente al clic, c’è un ritardo prima della chiusura e viene esposto un ritardo predefinito fisso o configurabile.

Scritto dal modello di indicizzazione a partire dal testo della issue.