docs-bug(Table): Add example with `rowspan`

### Documentation Feedback

There are many useful `Table` examples in the documentation. However, a common use case that’s missing is how to use `rowspan` to merge identical cells vertically.

For example, say we have the following data:

```ts
const ISOTOPE_DATA: PeriodicElement[] = [
{position: 1, element: 'Hydrogen', isotope: 'Protium', weight: 1.0078},
{position: 2, element: 'Hydrogen', isotope: 'Deuterium', weight: 2.0141},
{position: 3, element: 'Hydrogen', isotope: 'Tritium', weight: 3.016},
{position: 4, element: 'Helium', isotope: 'Helium-3', weight: 3.016},
{position: 5, element: 'Helium', isotope: 'Helium-4', weight: 4.0026},
];
```

We should be able to use it to create a table like this:

Element
Isotope
Weight


Hydrogen
Protium
1.0078


Deuterium
2.0141


Tritium
3.016


Helium
Helium-3
3.016


Helium-4
4.0026

This is related to https://github.com/angular/components/issues/11551, which is similar but for the `CdkTable` documentation.

### Affected documentation page

https://material.angular.dev/components/table/examples

Commencez par la page de documentation concernée, https://material.angular.dev/components/table/examples, et examinez les exemples de Table existants. Ajoutez un exemple utilisant les ISOTOPE_DATA fournis afin de montrer des cellules fusionnées verticalement avec rowspan, en reproduisant la disposition affichée de Hydrogen et Helium. La tâche est terminée lorsque la page explique clairement ce cas d’utilisation et l’affiche correctement.

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