interop-testing: Show full status for interop test failures

[ejona86]

It's pretty annoying to see a test failure with
"expected:<DEADLINE_EXCEEDED> but was:<INTERNAL>" and not know the description or throwable cause of the status. Introduce a convenience to include the full status on unexpected Status.Code. There were two usages of assertWithMessage() that did give nice errors; those were converted to this new utility.

It'd be even better to make a StatusSubject, but that'd take more time and this was easy and still an improvement. This was created because we're seeing servlet test failures with INTERNAL code, and we need to see the details.

[panchenko]

Can be a truth extension like the following

@NullMarked
public final class StatusSubject extends Subject {

  private final @Nullable Status actual;

  private StatusSubject(FailureMetadata metadata, @Nullable Status actual) {
    super(metadata, actual);
    this.actual = actual;
  }

  public void hasCode(Code expectedCode) {
    if (actual == null) {
      failWithoutActual(
          fact("expected to have code", expectedCode),
          simpleFact("but was null"));
    } else {
      check("getCode()").that(actual.getCode()).isEqualTo(expectedCode);
    }
  }

  public void hasCodeAndDescription(Code expectedCode, String expectedDescription) {
    if (actual == null) {
      failWithoutActual(
          fact("expected to have code", expectedCode),
          fact("and description", expectedDescription),
          simpleFact("but was null"));
    } else {
      check("getCode()").that(actual.getCode()).isEqualTo(expectedCode);
      check("getDescription()").that(actual.getDescription()).isEqualTo(expectedDescription);
    }
  }

  public static Factory<StatusSubject, Status> statuses() {
    return StatusSubject::new;
  }
}

and then assertAbout(statuses()).that(status).hasCode(Code.INVALID_ARGUMENT)