Add merge method to ArrayCollection

[dozsan]

Feature Request

The ArrayCollection-on class should have a merge method

Why

When I want to add ManyToMany items, the doctrine deletes them first and then adds them, but this can be used to prevent it from deleting what we don't want to delete

How

public function merge(Collection $collection): self
    {
        foreach ($this->getValues() as $element) {
            if (!$collection->contains($element)) {
                $this->removeElement($element);
            }
        }

        foreach ($collection as $element) {
            if (!$this->contains($element)) {
                $this->add($element);
            }
        }

        return $this;
    }