help(mat-date-range-picker): Getting date range values from Reactive FormGroup

#### What are you trying to do?

I would like to use the date range picker in a reactive form and emit an event when the FormGroup's value changes.

I'm subscribing to the valueChanges Observable on the FormGroup and emitting an event when a value changes.

#### What troubleshooting steps have you tried?

I am seeing many events being emitted when the FormGroup is initialized (4x). And when the form control's value is modified at runtime via button click there are even more events emitted.

Is a way to filter down the valueChange events coming from the FormGroup? I realize I could filter the values coming through the valueChange Observable but I'm not sure how to know which value is the one I'm after.

#### Reproduction
https://stackblitz.com/edit/date-time-picker-reactive-form?file=src/app/date-range-picker.ts

#### Environment

- Angular: 10.2.4
- CDK/Material: 10.2.7
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

Commencez par la reproduction StackBlitz liée, en particulier src/app/date-range-picker.ts, et suivez l’abonnement valueChanges de FormGroup de mat-date-range-picker pendant l’initialisation et les mises à jour des boutons. Confirmez si les émissions répétées sont un bug d’Angular Material ou le comportement attendu des formulaires réactifs ; l’issue ne spécifie aucune modification de code concrète ni aucun test permettant de considérer le travail comme terminé.

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