[GR-60237] Introduce serializable flag to reflection metadata

[graalvmbot]

Serialization metadata is now part of reflection metadata. For a type to be registered as serializable, the field "serializable" must be set to true inside of the type reflection registration. For example, the following reachability-metadata.json file:

{
  "reflection": [
    {
      "type": "fully.qualified.ClassName"
    }
  ],
  "serialization": [
    {
      "type": "fully.qualified.ClassName"
    }
  ]
}

can now be expressed with the much simpler:

{
  "reflection": [
    {
      "type": "fully.qualified.ClassName",
      "serializable": true
    }
  ]
}

As a side effect, types registered for serialization have to be explicitly registered for reflection as well. This was already done in the background, so the change has no image size impact.

[zakkak]

+1 That makes sense and interestingly it's similar to what Quarkus does.

@loicottet are there plans to backport this to GraalVM for JDK 21 as well?