default Set<String> names() {
        return bodyParts().stream()
                          .map(AggregatedBodyPart::name)
                          .collect(toImmutableSet());
    }
Returns the all control names of the body parts. The control
name is the {@code name} parameter of the {@code "content-disposition"}
header for a body part with disposition type {@code form-data}.
core/src/main/java/com/linecorp/armeria/common/multipart/AggregatedMultipart.java