Update examples to use classes from Symfony\Contracts\

[javiereguiluz]

This requires updating lots of use ... imports. For example:

• [DI] leverage Contracts\Service symfony#28207
• [Contracts] Add Cache contract to extend PSR-6 with tag invalidation, callback-based computation and stampede protection symfony#28096
• [Contracts] Add Translation\TranslatorInterface + decouple symfony/validator from symfony/translation symfony#28210
• ...

[javiereguiluz]

I'm closing this as fixed because some component already did the transition (Cache, Translation, ...) and the remaining ones have pending PRs (#11664 and #11665).