Merge #584: Getting ready to Qt 6 (5/n). Do not assume qDBusRegisterMetaType return type

6cf4dc7 qt: Do not assume `qDBusRegisterMetaType` return type (Hennadii Stepanov)

Pull request description:

  `qDBusRegisterMetaType` returns:
  - [`int`](https://doc.qt.io/qt-5/qdbusargument.html#qDBusRegisterMetaType) in Qt 5
  - [`QMetaType`](https://doc.qt.io/qt-6/qdbusargument.html#qDBusRegisterMetaType) in Qt 6

ACKs for top commit:
  laanwj:
    Anyhow code review ACK 6cf4dc7
  w0xlt:
    tACK 6cf4dc7 on Ubuntu 21.10, Qt 5.15.2.

Tree-SHA512: 17d43e191d31a6f927d19550c52471ed3b9222f492a23cee2e553f2c679cf37125e00637b00ea9f4ee3e37dfcf5278171be9a5e1e2e899592516291c7b5cd942

Author: hebasto

src/qt/notificator.cpp

@@ -14,8 +14,9 @@
 #include <QTemporaryFile>
 #include <QVariant>
 #ifdef USE_DBUS
-#include <stdint.h>
+#include <QDBusMetaType>
 #include <QtDBus>
+#include <stdint.h>
 #endif
 #ifdef Q_OS_MAC
 #include <qt/macnotificationhandler.h>
@@ -73,8 +74,6 @@ class FreedesktopImage
     FreedesktopImage() {}
     explicit FreedesktopImage(const QImage &img);
 
-    static int metaType();
-
     // Image to variant that can be marshalled over DBus
     static QVariant toVariant(const QImage &img);
 
@@ -136,15 +135,10 @@ const QDBusArgument &operator>>(const QDBusArgument &a, FreedesktopImage &i)
     return a;
 }
 
-int FreedesktopImage::metaType()
-{
-    return qDBusRegisterMetaType<FreedesktopImage>();
-}
-
 QVariant FreedesktopImage::toVariant(const QImage &img)
 {
     FreedesktopImage fimg(img);
-    return QVariant(FreedesktopImage::metaType(), &fimg);
+    return QVariant(qDBusRegisterMetaType<FreedesktopImage>(), &fimg);
 }
 
 void Notificator::notifyDBus(Class cls, const QString &title, const QString &text, const QIcon &icon, int millisTimeout)