Recent Scores: Add Guitar Pro file icon

Co-Authored-By: jessjwilliamson <71656189+jessjwilliamson@users.noreply.github.com>

src/project/project.qrc

@@ -45,6 +45,7 @@
         <file>qml/MuseScore/Project/internal/ProjectPropertiesBottomPanel.qml</file>
         <file>qml/MuseScore/Project/internal/ProjectPropertiesView.qml</file>
         <file>qml/MuseScore/Project/internal/PropertyItem.qml</file>
+        <file>resources/Placeholder_GP.png</file>
         <file>resources/Placeholder_MIDI.png</file>
         <file>resources/Placeholder_MXML.png</file>
         <file>resources/Placeholder_Other.png</file>

src/project/qml/MuseScore/Project/internal/ScoreItem.qml

@@ -233,6 +233,14 @@ FocusScope {
 
                 source: {
                     switch (root.suffix) {
+                    case "gtp":
+                    case "gp3":
+                    case "gp4":
+                    case "gp5":
+                    case "gpx":
+                    case "gp":
+                    case "ptb":
+                        return "qrc:/resources/Placeholder_GP.png"
                     case "mid":
                     case "midi":
                     case "kar":