Readd getter for MetadataFactory in Serialzier

[tgaertner]

Q	A
Bug report?	no
Feature request?	yes
BC Break report?	no
RFC?	no

Re-add getter for MetadataFactory in Serialzier to make it possible again to override metadata types like this: /** @var \JMS\Serializer\Metadata\PropertyMetadata $itemsMetadata */ $itemsMetadata = $this->serializer->getMetadataFactory()->getMetadataForClass(Content::class)->propertyMetadata['items']; $itemsMetadata->setType($type);

Expected Result

• This code worked in version 1.x and breaks ins version (2.x) 3.x

Actual Result

• Found no other way to achieve the desired type override.