Support template generics in PSALM class inheritance

[klesun]

Originally requested in #162 (comment)

Quoting @zmitic:

---

There is one minor issue, probably irrelevant. Because of nested-set requiring its own parent repository (not one from example under), I put code in trait like this:

class CityRepository extends ServiceEntityRepository
{
    /** @use RepositoryUtilsTrait<City> */
    use RepositoryUtilsTrait;

    public function __construct(ManagerRegistry $registry)
    {
        parent::__construct($registry, City::class);
    }
}

Trait itself:

    /**
     * @return ?T
     */
    public function getOneResultOrNull(Generator ...$generators)
    {
       // ...
    }

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