[Component][Serializer] Support hydrating an existing object in GetSetMethodNormalizer.

Hello, 

GetSetMethodNormalizer always instantiates the class, I modified the code so that it does not instantiate the class and allows to call the setters of an existing object. 

Tell me if this is interesting so that I update the PHPDoc too. 

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A