Fix context of Locator input

- In the main window, the locator input (actually the status bar)
  visually feels like being part of the mode widget, so give
  it its context.
- In extra editor windows, the whole editor window should have
  "editor manager" context, so that is also active for the locator
  input.

Task-number: QTCREATORBUG-20626
Task-number: QTCREATORBUG-20071
Change-Id: Ib68d6a8177446572ea59c3cc057eca0706173e11
Reviewed-by: Xing Xiong
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coreplugin/icore.cpp

@@ -531,6 +531,11 @@ QWidget *ICore::currentContextWidget()
     return context ? context->widget() : nullptr;
 }
 
+IContext *ICore::contextObject(QWidget *widget)
+{
+    return m_mainwindow->contextObject(widget);
+}
+
 
 QMainWindow *ICore::mainWindow()
 {