[REQ][java] Share common fields between Discriminator fields

Is your feature request related to a problem? Please describe.

We are using discriminator method in the interface for an openapi based spring code generator based on which we are generating the classes to be shared across.

Discriminator interface

@Schema(
        discriminatorMapping = {
                @DiscriminatorMapping(value = "type1", schema = Type1.class),
                @DiscriminatorMapping(value = "type2", schema = Type2.class),
                @DiscriminatorMapping(value = "type3", schema = Type3.class),
        },
        discriminatorProperty = "type",
        oneOf = {Type1.class,
                Type2.class,
                Type3.class
        }
)
public interface MainInterface {
        @Schema(
                requiredMode = Schema.RequiredMode.REQUIRED,
                example = "type1"
        )
        Type getType();

}

There properties that are shared across these Type child interfaces. So we want to add the shared getters in the MainInterface itself.

SharedProperties.java

public interface SharedProperties {
        String getName();
        String getDescription();
}

The generator currently generates main interface as

@JsonIgnoreProperties(
    value = {"type"},
    allowSetters = true
)
@JsonTypeInfo(
    use = Id.NAME,
    include = As.PROPERTY,
    property = "type",
    visible = true
)
@JsonSubTypes({@Type(
    value = Type1.class,
    name = "type1"
), @Type(
    value = Type2.class,
    name = "type2"
), @Type(
    value = Type3.class,
    name = "type3"
)})
public interface MainInterface {
    Type getType();
}

Describe the solution you'd like

We want to the Type interfaces to have SharedProperties methods. But we are not able to add it properly. Is there a way to implement this with keeping Type interfaces consistent to extend the Discriminator properties.

Describe alternatives you've considered

Tried add it as anyOf to MainInterface but discriminators are messing up and now Type classes doesn't implement MainInterface but it has all the properties from SharedProperties.

Additional context

Start with docs/generators/spring.md and trace how the Spring generator handles discriminator interfaces, oneOf, and generated Type interfaces. Done means shared getter methods are available on each Type interface while the types still implement MainInterface and retain discriminator behavior.