Add @ValidSubTypes

[SentryMan]

• adds a new annotation to extract subtype info from a class
• will generate a validator that uses instanceof (17) or pattern matching switch (21+) to redirect to the correct validator
• add Jstachio (compile-time templating is pretty handy)

Given

@SubTypes({ByQuerySelector.class, ByIdSelector.class})
public interface EntitySelector {}

The following is generated

@Generated("avaje-validation-generator")
public class EntitySelectorValidationAdapter implements ValidationAdapter<EntitySelector> {

  private final ValidationAdapter<ByQuerySelector> subAdapter0;
  private final ValidationAdapter<ByIdSelector> subAdapter1;

  public EntitySelectorValidationAdapter(ValidationContext ctx) {
    this.subAdapter0 = ctx.adapter(ByQuerySelector.class);
    this.subAdapter1 = ctx.adapter(ByIdSelector.class);
  }

  @Override
  public boolean validate(EntitySelector value, ValidationRequest request, String field) {
    return switch(value) {
      case null -> true;
      case ByQuerySelector val -> subAdapter0.validate(val, request, field);
      case ByIdSelector val -> subAdapter1.validate(val, request, field);
      default -> true;
    };

  }
}

Fixes #279

[rbygrave]

Pondering if @SubTypes should be more @ValidSubtypes in that people reading the code will have to look at the package to know that its related to validation per se.

[SentryMan]

Never said I was great at naming, feel free to change