Merge "Replace ":strings" with "strings"" into main

// TODO(scottjonathan): Replace with generic set implementation

final class StringSetPolicySerializer extends PolicySerializer<Set<String>> {

    private static final String ATTR_VALUES = ":strings";

    private static final String ATTR_VALUES = "strings";

    private static final String ATTR_VALUES_SEPARATOR = ";";

    @Override

    void saveToXml(PolicyKey policyKey, TypedXmlSerializer serializer,

            @NonNull Set<String> value) throws IOException {