STC: fix support for unbounded wildcard references to self-bounded type parameters

@Grab('org.springframework.boot:spring-boot-starter-webflux:2.6.7')
import org.springframework.core.ParameterizedTypeReference
import org.springframework.http.MediaType
import org.springframework.web.reactive.function.client.WebClient

import java.time.Duration

@groovy.transform.CompileStatic
class WebFluxFluentApiBugTest {

  private static final ParameterizedTypeReference<List<BigDecimal>> TYPE_TAG
    = new ParameterizedTypeReference<List<BigDecimal>>() {}

  private static final Duration MAX_DURATION = Duration.ofSeconds(8)

  private final WebClient webClient

  List<BigDecimal> flux() {
    def response = webClient.get()
      .uri('/something?id={id}', 'id')
      .accept(MediaType.APPLICATION_JSON)
      .retrieve()
      .toEntity(TYPE_TAG)
      .block(MAX_DURATION)
    return response.getBody() ?: []
  }
}