[Serializer] Name converter support

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #12212
| License       | MIT
| Doc PR        | not yet

This PR adds support for custom property naming strategies to the serializer and provides a built-in NameConverter using this new system: (CamelCase to underscore).
It handles normalization and denormalization (convert `fooBar` to `foo_bar` when serializing, then from `foo_bar` to `fooBar` when deserializing). It also has a flag to convert only some attributes.

The `setCamelizedAttributes()` is deprecated in favor of this new method (more flexible, allows to rename all attributes of a class and support deserialization) and now uses it internally.

Ok changed.