Finish supporting autoBuild vs build

[ZacSweers]

Currently this snippet will generate the autoBuild() method but not the build() method

@AutoValue.Builder
public abstract static class Builder {
  public abstract Builder image48(String image48);

  public abstract Builder image64(String image64);

  public abstract Builder image72(String image72);

  abstract AppIcons autoBuild();

  public AppIcons build() {
    return autoBuild();
  }
}