[Workflow] Introduce a Workflow interface, type-hint against it in Registry #23910
Description
| Q | A |
|---|---|
| Bug report? | no |
| Feature request? | yes |
| BC Break report? | no |
| RFC? | yes |
| Symfony version | latest |
Workflow\Registry accepts only instances of Worflow\Workflow which makes decorating workflows awkward. It would allow for more flexibility if an interface was introduced here.