feat: Infer discriminator mapping

[PatrickFeiring]

Description

This PR adds inference of discriminator mappings when an explicit mapping is not present.

It should greatly reduce the need for explicit @DiscriminatorMapping annotations and make it easier to keep the mapping in sync.

The basic theme of the approach is to leave as much resolving to Jackson as possible. This is done by instantiating a type serializer for the class, and leting Jackson compute the ids used in the mapping. This means that type ids from all the following sources are supported

• name field in @JsonSubTypes.Type annotations
• @JsonTypeName annotations
• Mechanisms given by JsonTypeInfo.Id in @JsonTypeInfo annotations

Mappings are computed not only for sub types listed explicitly in JsonSubTypes annotations, but should also for modules that customize the AnnotationInstrospectors findSubtypes method, such as https://github.com/sigpwned/jackson-modules-java-17-sealed-classes.

Closes: #3411

Type of Change

• 🐛 Bug fix
• ✨ New feature
• ♻️ Refactor (non-breaking change)
• 🧪 Tests
• 📝 Documentation
• 🧹 Chore (build or tooling)

Checklist

• I have added/updated tests as needed
• I have added/updated documentation where applicable
• The PR title is descriptive
• The code builds and passes tests locally
• I have linked related issues (if any)

Screenshots / Additional Context