parameterConsistency field not deserializable from YAML

[benbellick]

YAML extension files containing parameterConsistency in variadic function definitions fail to load with the error:

Unrecognized field "parameterConsistency" (class ImmutableSimpleExtension$VariadicBehavior$Json),
not marked as ignorable (2 known properties: "min", "max"])

As a minimal test case to demonstrate the failure:

@Test
public void testParameterConsistencyLoading() {
  String yamlContent =
      "urn: extension:test:example\n"
          + "scalar_functions:\n"
          + "  - name: test_func\n"
          + "    impls:\n"
          + "      - args:\n"
          + "          - name: arg1\n"
          + "            value: string\n"
          + "        variadic:\n"
          + "          min: 1\n"
          + "          parameterConsistency: CONSISTENT\n"
          + "        return: string\n";

  SimpleExtension.ExtensionCollection collection =
      SimpleExtension.load("test://example", yamlContent);

  assertEquals(
      SimpleExtension.VariadicBehavior.ParameterConsistency.CONSISTENT,
      collection.scalarFunctions().get(0).variadic().get().parameterConsistency());
}

This can be fixed by adding the @Value.Default annotation to the VariadicBehavior.parameterConsistency() method. Without it, the Immutables library cannot recognize it as a deserializable field.

This will need one extra step, which is to actually thread the parameterConsistency info through to the function validation to ensure that the parameterConsistency is actually enforced.