QmlDesigner: Add delete action to 3D Editor's context menu

This entails selecting a model upon right-clicking if it is not selected.
Also fixed a memory leak and small tweaks.

Fixes: QDS-7401
Change-Id: I592acb3fff30ecc3236f3cf2fbe126de4fb389dc
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>

src/plugins/qmldesigner/components/edit3d/edit3dview.cpp

@@ -249,6 +249,10 @@ void Edit3DView::customNotification(const AbstractView *view, const QString &ide
 void Edit3DView::modelAtPosReady(const ModelNode &modelNode)
 {
     if (m_modelAtPosReqType == ModelAtPosReqType::ContextMenu) {
+        // Make sure right-clicked item is selected. Due to a bug in puppet side right-clicking an item
+        // while the context-menu is shown doesn't select the item.
+        if (modelNode.isValid() && !modelNode.isSelected())
+            setSelectedModelNode(modelNode);
         m_edit3DWidget->showContextMenu(m_contextMenuPos, modelNode);
     } else if (m_modelAtPosReqType == ModelAtPosReqType::MaterialDrop) {
         if (m_droppedMaterial.isValid() && modelNode.isValid()) {

src/plugins/qmldesigner/components/edit3d/edit3dwidget.cpp

@@ -185,7 +185,12 @@ void Edit3DWidget::createContextMenu()
         ModelNodeOperations::editMaterial(selCtx);
     });
 
-    // TODO: add more actions: delete, create, etc
+    m_deleteAction = m_contextMenu->addAction(tr("Delete"), [&] {
+        view()->executeInTransaction("Edit3DWidget::createContextMenu", [&] {
+            for (ModelNode &node : m_view->selectedModelNodes())
+                node.destroy();
+        });
+    });
 }
 
 void Edit3DWidget::contextHelp(const Core::IContext::HelpCallback &callback) const
@@ -241,6 +246,7 @@ void Edit3DWidget::showContextMenu(const QPoint &pos, const ModelNode &modelNode
     m_contextMenuTarget = modelNode;
 
     m_editMaterialAction->setEnabled(modelNode.isValid());
+    m_deleteAction->setEnabled(modelNode.isValid());
 
     m_contextMenu->popup(mapToGlobal(pos));
 }

src/plugins/qmldesigner/components/edit3d/edit3dwidget.h

@@ -76,6 +76,7 @@ private:
     QPointer<QMenu> m_backgroundColorMenu;
     QPointer<QMenu> m_contextMenu;
     QPointer<QAction> m_editMaterialAction;
+    QPointer<QAction> m_deleteAction;
     ModelNode m_contextMenuTarget;
 };