Use window title, or custom title widget if it's set. Remove 'title'
property.
Update demos and tests to set the title on the window instead of
headerbar.
Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.
Applications need a way to fix or adapt the decoration layout,
for situations like split header bars. Setting the layout from
the theme with a style property did not offer a good way to do
this, and the ::show-close-button property does not provide
fine-grained control.
To improve the situation, move the layout string to a property of
GtkHeaderBar which is backed by a setting. This allows platforms to
set a default button layout independent of the theme, while applications
can override the default.
The style GtkWindow style property is now deprecated and ignored.
It is a fairly common case to just want a title, and not
reserve extra space for a subtitle. This is much easier
to get right by setting a boolean property than by
constructing a custom title widget.
Allow showing the fallback app menu with a menu button
in the header bar. Applications have to explicitly enable
this by calling gtk_header_bar_set_show_fallback_app_menu.
Add a boolean property that controls whether a window close button
will be shown in the header bar or not. Doing this in the toolkit
will ensure consistency of the visual apperance.
https://bugzilla.gnome.org/show_bug.cgi?id=702971
