title_widget
Description:
The title widget to display.
When set to `NULL`, the header bar will display the title of the window it is contained in.
To use a different title, use [class@WindowTitle]:
```xml <object class="AdwHeaderBar"> <property name="title-widget"> <object class="AdwWindowTitle"> <property name="title" translatable="yes">Title</property> </object> </property> </object> ```