window: Add hide-titlebar-when-maximized property

window: Add hide-titlebar-when-maximized property

For maximized windows, titlebars cannot be used to reposition or
scale the window, so if an application does not use it to convey
useful information (other than the application name), the screen
space occupied by titlebars could be put to better use.
Add a new window property which requests from the window manager
to hide titlebars when windows are maximized to account for this.

https://bugzilla.gnome.org/show_bug.cgi?id=665616