[FIXED JENKINS-42521] Add RunWrapper.getCurrentResult()

getCurrentResult() will never be null - if build().getResult() is
null, it'll return Result.SUCCESS.toString(). In a perfect world, I'd
change RunWrapper.getResult() to this behavior, but that'd possibly
break existing logic out in the wild, so a new method it is.

src/main/java/org/jenkinsci/plugins/workflow/support/steps/build/RunWrapper.java

@@ -121,6 +121,12 @@ public int getNumber() throws AbortException {
        return result != null ? result.toString() : null;
    }

    @Whitelisted
    public @Nonnull String getCurrentResult() throws AbortException {
        Result result = build().getResult();
        return result != null ? result.toString() : Result.SUCCESS.toString();
    }

    @Whitelisted
    public long getTimeInMillis() throws AbortException {
        return build().getTimeInMillis();

src/test/java/org/jenkinsci/plugins/workflow/support/steps/build/RunWrapperTest.java

@@ -166,6 +166,24 @@
        });
    }

    @Issue("JENKINS-37366")
    @Test public void getCurrentResult() {
        r.addStep(new Statement() {
            @Override public void evaluate() throws Throwable {
                MockFolder folder = r.j.createFolder("this-folder");
                WorkflowJob p = folder.createProject(WorkflowJob.class, "current-result-job");
                p.setDefinition(new CpsFlowDefinition(
                        "echo \"initial currentBuild.currentResult='${currentBuild.currentResult}'\"\n" +
                        "currentBuild.result = 'UNSTABLE'\n" +
                        "echo \"final currentBuild.currentResult='${currentBuild.currentResult}'\"\n",
                        true));
                WorkflowRun b = r.j.assertBuildStatus(Result.UNSTABLE, p.scheduleBuild2(0).get());
                r.j.assertLogContains("initial currentBuild.currentResult='" + Result.SUCCESS.toString() + "'", b);
                r.j.assertLogContains("final currentBuild.currentResult='" + Result.UNSTABLE.toString() + "'", b);
            }
        });
    }

    // Like org.hamcrest.text.MatchesPattern.matchesPattern(String) but doing a substring, not whole-string, match:
    private static Matcher<String> containsRegexp(final String rx) {
        return new SubstringMatcher(rx) {