fix: existing wm titlebar

  It's unload dxcb platform plugin, and it's an change for qt,
using `QDir().entryList()` to find plugin in qt6.2 before,
and using `QDirIterator()` to find in qt6.2 after.
QDir will sort result by name default, which is like `ls`,
and QDirIterator doesn't sort result, which is like `ls -U`.
  now we fix it in application temporarily.

Issue: linuxdeepin/developer-center#6686

CMakeLists.txt

@@ -118,6 +118,7 @@ PRIVATE
 target_link_libraries(${BIN_NAME} PRIVATE
     ${DTK_NS}::Core
     ${DTK_NS}::Gui
+    Qt::GuiPrivate
     Qt::Qml
     Qt::Quick
     Qt::QuickControls2

debian/control

@@ -10,6 +10,7 @@ Build-Depends:
 # v-- to get systemduserunitdir from its pkg-config data
  systemd,
  qt6-base-dev,
+ qt6-base-private-dev,
  qt6-svg-dev,
  qt6-declarative-dev,
  qt6-tools-dev,

main.cpp

@@ -24,14 +24,29 @@
 #include <launcherfoldericonprovider.h>
 #include <blurhashimageprovider.h>
 #include <multipagesortfilterproxymodel.h>
+#include <qpa/qplatformintegrationfactory_p.h>
 
 DCORE_USE_NAMESPACE
 DGUI_USE_NAMESPACE
 
+void tryUpdatePlatformPluginToDXcb()
+{
+    if (qEnvironmentVariableIsSet("WAYLAND_DISPLAY"))
+        return;
+
+    const QByteArray dxcb = QByteArrayLiteral("dxcb");
+    if (QPlatformIntegrationFactory::keys().contains(dxcb) &&
+            qEnvironmentVariableIsEmpty("QT_QPA_PLATFORM")) {
+        qputenv("QT_QPA_PLATFORM", dxcb);
+    }
+}
+
 int main(int argc, char* argv[])
 {
     // workaround for https://github.com/linuxdeepin/dtk/issues/115
     qputenv("D_POPUP_MODE", "embed");
+    // TODO qxcb maybe found firstly in qt6.4 later.
+    tryUpdatePlatformPluginToDXcb();
 
     QGuiApplication app(argc, argv);
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)