Deprecate the internal Symfony dispatcher adapter #21848
                
     Merged
            
            
          
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This type is not known on the public API, yet we should make sure that
any usage of this class is noticed and migrated as soon as possible.
IMO deprecation makes sense for internals as well as phpstorm and other decent IDEs show deprecated API usages in a distinctive styling.
Related to #21322, the change of the public API.