kcms/tabbox: Use higher resolution thumbnails for previews

Replace the hardcoded thumbnails which have a low resolution for
current screen standards (~300x200), with higher resolution ones
(~1200x800).

Also set the new 6.0 wallpaper as the fallback desktop thumbnail

BUG: 446765
FIXED-IN: 5.93.0

src/kcms/tabbox/CMakeLists.txt

@@ -31,7 +31,7 @@ target_link_libraries(kcm_kwintabbox
 )
 
 ########### install files ###############
-install(FILES thumbnails/konqueror.png
+install(FILES thumbnails/falkon.png
               thumbnails/kmail.png
               thumbnails/systemsettings.png
               thumbnails/dolphin.png

src/kcms/tabbox/thumbnailitem.cpp

@@ -42,7 +42,7 @@ void WindowThumbnailItem::findImage()
     QString imagePath;
     switch (m_wId) {
     case Konqueror:
-        imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kwin/kcm_kwintabbox/konqueror.png");
+        imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kwin/kcm_kwintabbox/falkon.png");
         break;
     case Systemsettings:
         imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kwin/kcm_kwintabbox/systemsettings.png");
@@ -54,7 +54,7 @@ void WindowThumbnailItem::findImage()
         imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kwin/kcm_kwintabbox/dolphin.png");
         break;
     case Desktop:
-        imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "wallpapers/Next/contents/screenshot.png");
+        imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "wallpapers/Next/contents/images/1280x800.png");
         if (imagePath.isNull()) {
             imagePath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, "kwin/kcm_kwintabbox/desktop.png");
         }