static ComplexType.Builder builder() {
      return new AutoValue_SerializableAutoValueExtensionTest_ComplexType.Builder();
    }
Type that may result in nested lambdas in the generated code. Including this allows us to
verify that we handle those correctly, in particular not reusing a lambda parameter name in
another lambda nested inside the first one.
value/src/test/java/com/google/auto/value/extension/serializable/processor/SerializableAutoValueExtensionTest.java