WIP: Avoid using deprecated `QGuiApplication::paletteChanged`

Unfortunately this doesn't work; the `QEvent::ApplicationPaletteChange`
event is never received.

syncthingmodel/syncthingicons.cpp

@@ -9,6 +9,7 @@
 
 #include <qtforkawesome/icon.h>
 
+#include <QEvent>
 #include <QFile>
 #include <QGuiApplication>
 #include <QPainter>
@@ -16,6 +17,8 @@
 #include <QStringBuilder>
 #include <QSvgRenderer>
 
+#include <iostream>
+
 #ifndef LIB_SYNCTHING_MODEL_STATIC
 ENABLE_QT_RESOURCES_OF_STATIC_DEPENDENCIES
 #endif
@@ -315,17 +318,8 @@ IconManager::IconManager(const QPalette *palette)
     , m_trayIcons(m_statusIcons)
     , m_commonForkAwesomeIcons(
           m_forkAwesomeRenderer, (palette ? *palette : QGuiApplication::palette()).color(QPalette::Normal, QPalette::Text), QSize(64, 64))
+    , m_usesApplicationPalette(palette == nullptr)
 {
-#ifdef __GNUC__
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
-#endif
-    if (!palette) {
-        QObject::connect(qGuiApp, &QGuiApplication::paletteChanged, this, &IconManager::setPalette);
-    }
-#ifdef __GNUC__
-#pragma GCC diagnostic pop
-#endif
 }
 
 void IconManager::setPalette(const QPalette &palette)
@@ -334,6 +328,19 @@ void IconManager::setPalette(const QPalette &palette)
         m_commonForkAwesomeIcons = ForkAwesomeIcons(m_forkAwesomeRenderer, palette.color(QPalette::Normal, QPalette::Text), QSize(64, 64)));
 }
 
+bool IconManager::event(QEvent *event)
+{
+    switch (event->type()) {
+    case QEvent::ApplicationPaletteChange:
+        std::cout << "this is unfortunately never executed" << std::endl;
+        setPalette(QGuiApplication::palette());
+        break;
+    default:
+        ;
+    }
+    return QObject::event(event);
+}
+
 IconManager &IconManager::instance(const QPalette *palette)
 {
     static auto iconManager = IconManager(palette);

syncthingmodel/syncthingicons.h

@@ -166,6 +166,9 @@ Q_SIGNALS:
     void statusIconsChanged(const Data::StatusIcons &newStatusIcons, const Data::StatusIcons &newTrayIcons);
     void forkAwesomeIconsChanged(const Data::ForkAwesomeIcons &newForkAwesomeIcons);
 
+protected:
+    bool event(QEvent *event) override;
+
 private:
     explicit IconManager(const QPalette *palette = nullptr);
 
@@ -173,6 +176,7 @@ private:
     StatusIcons m_trayIcons;
     QtForkAwesome::Renderer m_forkAwesomeRenderer;
     ForkAwesomeIcons m_commonForkAwesomeIcons;
+    bool m_usesApplicationPalette;
 };
 
 inline void IconManager::applySettings(const StatusIconSettings *statusIconSettings, const StatusIconSettings *trayIconSettings)