TaskTree: Rename optional into finishAllAndDone

Rationale:
1. More descriptive.
2. More consistent with a planned new finishAllAndError policy.
3. Limits the possibilities of making a conflict with std::optional.

Change-Id: I5155630188e4b699e6c18b13a101e0e2d4fe98f2
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/autotest/testrunner.cpp

@@ -347,7 +347,7 @@ void TestRunner::runTestsHelper()
         std::unique_ptr<TestOutputReader> m_outputReader;
     };
 
-    QList<TaskItem> tasks{optional};
+    QList<TaskItem> tasks{finishAllAndDone};
 
     for (ITestConfiguration *config : m_selectedTests) {
         QTC_ASSERT(config, continue);
@@ -442,7 +442,7 @@ void TestRunner::runTestsHelper()
             }
         };
         const Group group {
-            optional,
+            finishAllAndDone,
             Storage(storage),
             onGroupSetup(onSetup),
             ProcessTask(onProcessSetup, onProcessDone, onProcessDone)