[Security] [Doctrine] Added BaseUserProviderInterface

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11157 
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/issues/4543

You can now implement BaseUserProviderInterface without the need of implementing `supportsClass` function.
Is it really needed to move the `refreshUser()` method to the base interface too? Usually you would have users that have an identifier which can be passed to the repository's `find()` method, wouldn't you?