feat(COMPONENT): Add matNoDataNode Directive to <mat-tree> for Handling Empty States

### Feature Description

Currently, Angular Material's component does not provide a built-in way to handle empty states (e.g., when the data source has no nodes). Developers must manually add conditional logic in their templates to display a "No records found" or similar message.

This feature request proposes adding a `matNoDataNode `directive to , similar to the `matNoDataRow `directive available for tables. The `matNoDataNode `directive would allow developers to define a template that is displayed when the tree's data source is empty.

Proposed Implementation:

- A new directive, `matNoDataNode`, that conditionally renders a template when the tree's data source is empty.

- Seamless integration with the existing mat-tree API, ensuring consistency with other Angular Material components.

### Use Case

he `matNoDataNode `directive would enable the following use cases:

1. Displaying a "No Records Found" Message

When a tree has no data, developers can use `matNoDataNode `to display a user-friendly message, such as "No records found" or "No data available."

Example:

```

{{ node.name }}

```

2. Custom Empty-State Templates

Developers can define custom templates for empty states, including icons, buttons, or additional instructions.

Example:

```

```

Commencez par localiser l’implémentation existante de mat-tree et la directive matNoDataRow utilisée par les tableaux, puis examinez comment leurs tests couvrent les sources de données vides. Définissez le comportement de l’arbre pour les données vides et non vides, ajoutez la directive et ses tests, et vérifiez que le template ne s’affiche que lorsque l’arbre ne contient aucun nœud.

Rédigé par le modèle d'indexation à partir du texte de l'issue.