ProjectExplorer: Make sure to keep focus on the project tree

... after renaming files.
The problem was as follows:
  - The user renames e.g. a header file myclass.h, resulting in a focus
    change to a newly created line edit.
  - We ask them whether myclass.cpp should also be renamed, resulting in
    a focus change to the message box.
  - After the message box closes, the line edit gets destroyed before
    the focus can change back to it.
  - The focus goes to some random widget.
Prevent this by explicitly giving the project tree widget the focus when
the line edit gets destroyed.

Fixes: QTCREATORBUG-30926
Change-Id: I36ae61219ce59966d3758c4614e3c49d286af160
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/projectexplorer/projecttreewidget.cpp

@@ -100,6 +100,19 @@ public:
         }
     }
 
+    void destroyEditor(QWidget *editor, const QModelIndex &index) const final
+    {
+        // QTCREATORBUG-30926
+        for (QWidget *p = editor->parentWidget(); p; p = p->parentWidget()) {
+            if (qobject_cast<ProjectTreeWidget *>(p)) {
+                p->setFocus();
+                break;
+            }
+        }
+
+        QStyledItemDelegate::destroyEditor(editor, index);
+    }
+
 private:
     ProgressIndicatorPainter *findOrCreateIndicatorPainter(const QModelIndex &index) const
     {