[DeadCode] Keep generic @var/@return self<...> narrowing annotations

[TomasVotruba]

Fixes rectorphp/rector#9793

Two DeadCode rules stripped valid generic type annotations that narrow the return type of a generic class via template specialization. The @var self<...> / @return self<...> add information that the native self type / new self() cannot express, so they must be kept.

RemoveNonExistingVarAnnotationRector

An empty-name @var before return new self(...) was removed, because New_ returns were explicitly excluded (a plain @var array<...> on new stdClass really is unwanted). Now it is kept when the @var is a generic type over the instantiated class.

 final class Result
 {
     public static function success(mixed $value = null): self
     {
         /** @var self<TSuccessValue, never> */
         return new self(true, value: $value);
     }
 }

Before: the docblock was removed. After: kept.

A mismatched annotation such as /** @var array<string, string> */ return new stdClass; is still removed (base type array != stdClass).

RemoveDuplicatedReturnSelfDocblockRector

@return self<...> maps to a GenericObjectType (subclass of ObjectType) whose class name equals the current class, so it was treated as a duplicate of the native self return type and removed. Generic doc types are now skipped.

 final class Result
 {
     /**
      * @return self<TSuccessValue, never>
      */
     public function success(): self
     {
         return $this;
     }
 }

Before: the docblock was removed. After: kept. Bare @return self / @return $this / @return static are still removed as before.

Tests

New skip fixtures for both rules covering the generic case.

[TomasVotruba]

LGTM 👍