[HttpKernel] [FrameworkBundle] - Added interface to register commands instead of depending on Bundle class

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

- [ ] submit changes to the documentation

This feature introduce a new interface to trigger the registration of commands on Bundles that do not extends `Symfony\Component\HttpKernel\Bundle\Bundle`.

Using this PR, Bundles can now implement `Symfony\Component\HttpKernel\Bundle\BundleInterface` and `Symfony\Component\HttpKernel\Bundle\CommandRegisterInterface` to enable command register by the FrameworkBundle's Application class.

ah sorry, I missed the fact that you don't mock the class but instantiate it. But then, you should at least implement getName properly (returning null does not respect the interface as it asks for a string)