QtSupport: Restrict QtVersionManagerImpl lifetime to plugin lifetime

This occasionally triggered crashes on static destruction when
hard-killing Qt Creator.

Giving QtVersionManagerImpl the plugin as QObject parent effectively
re-instates the lifetime behavior from before we moved to delayed
initialization. We keep the delayed initialization, at the (acceptable)
prize of a somewhat quirky setup.

Change-Id: I1b4be284a1b573325ed5cc441778eeb48b94c24b
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/qtsupport/qtsupportplugin.cpp

@@ -83,6 +83,8 @@ void QtSupportPlugin::initialize()
     addTestCreator(createQtProjectImporterTest);
 #endif
 
+    setupQtVersionManager(this);
+
     setupDesktopQtVersion();
     setupEmbeddedLinuxQtVersion();
     setupGettingStartedWelcomePage();

src/plugins/qtsupport/qtversionmanager.cpp

@@ -89,7 +89,8 @@ static PersistentSettingsWriter *m_writer = nullptr;
 class QtVersionManagerImpl : public QObject
 {
 public:
-    QtVersionManagerImpl()
+    QtVersionManagerImpl(QObject *parent)
+        : QObject(parent)
     {
         qRegisterMetaType<FilePath>();
 
@@ -135,10 +136,18 @@ public:
     QTimer m_fileWatcherTimer;
 };
 
+static QObject *s_guard = nullptr;
+
+void Internal::setupQtVersionManager(QObject *guard)
+{
+    s_guard = guard;
+}
+
 QtVersionManagerImpl &qtVersionManagerImpl()
 {
-    static QtVersionManagerImpl theQtVersionManager;
+    QTC_CHECK(s_guard);
-    return theQtVersionManager;
+    static auto theQtVersionManager = new QtVersionManagerImpl(s_guard);
+    return *theQtVersionManager;
 }
 
 void QtVersionManagerImpl::triggerQtVersionRestore()

src/plugins/qtsupport/qtversionmanager.h

@@ -70,4 +70,6 @@ private:
     static int getUniqueId();
 };
 
+namespace Internal { void setupQtVersionManager(QObject *guard); }
+
 } // namespace QtSupport