Fix outdated Unicode requirements check

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it needs to replace TODO with real CR and add deprecation test

Also there's some usage in contrib

- http://codcontrib.hank.vps-private.net/search?text=Unicode%3A%3AgetStatu...
- http://codcontrib.hank.vps-private.net/search?text=Unicode%3A%3Acheck%28...
- http://codcontrib.hank.vps-private.net/search?text=Unicode%3A%3ASTATUS_M...

Probably constants should be deprecated too as modules can do extension_loaded('mbstring')

OTOH there's polyfill shipped with core

core$ composer why symfony/polyfill-mbstring
phootwork/lang          v3.2.2 requires symfony/polyfill-mbstring (^1.12) 
symfony/console         v6.3.0 requires symfony/polyfill-mbstring (~1.0)  
symfony/dom-crawler     v6.3.0 requires symfony/polyfill-mbstring (~1.0)  
symfony/filesystem      v6.3.0 requires symfony/polyfill-mbstring (~1.8)  
symfony/http-foundation v6.3.0 requires symfony/polyfill-mbstring (~1.1)  
symfony/mime            v6.3.0 requires symfony/polyfill-mbstring (^1.0)  
symfony/string          v6.3.0 requires symfony/polyfill-mbstring (~1.0)  
symfony/validator       v6.3.0 requires symfony/polyfill-mbstring (~1.0)  
symfony/var-dumper      v6.3.0 requires symfony/polyfill-mbstring (~1.0)  
twig/twig               v3.6.0 requires symfony/polyfill-mbstring (^1.3)