Gui: offer possibility to editing view provider to handle "Select All" command

src/Mod/Sketcher/Gui/ViewProviderSketch.cpp

@@ -2588,6 +2588,12 @@ void ViewProviderSketch::updateColor()
     editCoinManager->updateColor();
 }
 
+bool ViewProviderSketch::selectAll()
+{
+    // TODO: eventually implement "select all" logic
+    return true;
+}
+
 bool ViewProviderSketch::doubleClicked()
 {
     Gui::Application::Instance->activeDocument()->setEdit(this);

src/Mod/Sketcher/Gui/ViewProviderSketch.h

@@ -656,6 +656,9 @@ public:
     {
         return nullptr;
     }
+    /// is called when the provider is in edit and a "Select All" command was issued
+    /// Provider shall return 'false' is it ignores the command, 'true' otherwise
+    bool selectAll() override;
     /// is called by the tree if the user double clicks on the object
     bool doubleClicked() override;
     /// is called when the Provider is in edit and the mouse is moved