Describe the bug
During the schema generation, building the code registry checks the WiringFactory to see if it can provide an item before checking explicitly registered items. This seems counter-intuitive. I would expect explicit registration of a data fetcher, type resolver, scalars, etc... to have the highest priority.

I think this could be as simple as reversing the if/else checks here to look for an explicit one first, then factory:

Scalars: https://github.com/graphql-java/graphql-java/blob/v20.1/src/main/java/graphql/schema/idl/SchemaGeneratorHelper.java#L438-L443

Interface type resolvers: https://github.com/graphql-java/graphql-java/blob/v20.1/src/main/java/graphql/schema/idl/SchemaGeneratorHelper.java#L504-L514

Union type resolvers: https://github.com/graphql-java/graphql-java/blob/v20.1/src/main/java/graphql/schema/idl/SchemaGeneratorHelper.java#L526-L536

Data Fetchers: https://github.com/graphql-java/graphql-java/blob/v20.1/src/main/java/graphql/schema/idl/SchemaGeneratorHelper.java#L836-L841

To Reproduce

Create wiring and register both an explicit type resolver in addition to a wiring factory.

var factory = new WiringFactory() {
  @Override
  public boolean providesTypeResolver(InterfaceWiringEnvironment environment) {
    return true;
  }

  @Override
  public TypeResolver getTypeResolver(InterfaceWiringEnvironment environment) {
    return env -> env.getSchema().getQueryType();
  }
};

var wiring = RuntimeWiring.newRuntimeWiring()
    .wiringFactory(factory)
    .type(TypeRuntimeWiring.newTypeWiring("MyType").typeResolver(env -> "FooType"))
    .build();

When we query for something that returns MyType, we will receive an error about failing to resolve MyType to a concrete implementation.