Map<String, PropertyBuilder> propertyNameToPropertyBuilder() {
    return propertyNameToPropertyBuilder;
  }
Returns a multimap from the name of a property to the methods that set it. If the property is
defined by an abstract method in the {@code @AutoValue} class called {@code foo()} or {@code
getFoo()} then the name of the property is {@code foo} and there will be an entry in the map
where the key is {@code "foo"} and the value describes a method in the builder called {@code
foo} or {@code setFoo}.
value/src/main/java/com/google/auto/value/processor/BuilderMethodClassifier.java