icon fallback concept without QIcon::fallbackSearchPaths (bug #62106) * FigureWindow.cc (FigureWindow): do not use fromTheme * ToolBarButton.cc: include QString and gui-preferences-global.h; (get_icon): do not use fromTheme * gui-preferences-global.h: define QStringList with exisiting icon fallback paths togehter with an enumeration for the list inidices * octave-dock-widget.cc (label_dock_widget): use ressource_manager::icon instead of fromTheme, use constants from gui-preferences for icon paths instead of literal strings in style sheets (make_window): dito (make_widget): dito * resource-manager.cc (resource_manager): initialize m_icon_fallbacks; (config_icon_theme): collect fallback paths in a string list depending on selected icon theme; (icon): test existance of icon in current theme, if not, test the fallback locations; * resource-manager.h: new string list m_icon_fallbacks

--- a/libgui/src/gui-preferences-global.h	Thu Feb 24 17:33:44 2022 +0100
+++ b/libgui/src/gui-preferences-global.h	Thu Feb 24 22:16:35 2022 +0100
@@ -84,6 +84,22 @@
 const gui_pref
 global_icon_theme ("use_system_icon_theme", QVariant (true));
 
+enum
+{
+  ICON_THEME_SYSTEM,
+  ICON_THEME_OCTAVE,
+  ICON_THEME_TANGO,
+  ICON_THEME_CURSORS
+};
+
+const QStringList
+global_icon_fallback_paths (QStringList ()
+                        << ""
+                        << ":/icons/octave/128x128/"
+                        << ":/icons/tango/128x128/"
+                        << ":/cursors/"
+                       );
+
 // Other
 
 const gui_pref