docs-bug(chips): the "form example" is not fully related to forms

### Documentation Feedback

We have `chips-form-control-example`, `chips-reactive-form-example` components that intend to illustrate how chips interact with the form control.
I see 2 problems here.

1. The interaction with `mat-chip-grid` is happening not fully through the formControl. For now the source of chips's list is `keywords` signal, not the formControl: `@for (keyword of keywords(); track keyword) {`
It seems we should take the formControl as the source of chips's list (not the signal): `@for (keyword of formControl.value || []; track keyword) {`
Moreover we could get rid of the signal, because the goal of the example is to show the interaction between the formControl and the chips in the template.

2. These two examples of `chips-form-control-example` and `chips-reactive-form-example` components duplicate each other. They have the same logic inside of components classes. So it seems we could leave only one of these two examples.

### Affected documentation page

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

Commencez par les composants chips-form-control-example et chips-reactive-form-example référencés dans l’issue, puis examinez les exemples présentés sur la page de documentation de chips. Comparez leurs classes et leurs templates ; le travail est terminé lorsque la liste de chips est présentée via le formControl plutôt que via le keywords signal et que l’exemple en double est supprimé ou regroupé.

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