Merge branch 'wip/otte/monitors' into 'master'

various GDK cleanups

See merge request GNOME/gtk!1920

diff --cc docs/reference/gtk/migrating-3to4.xml
Simple merge

diff --cc gdk/broadway/gdkdisplay-broadway.c
Simple merge

diff --cc gdk/broadway/gdkdisplay-broadway.h
Simple merge

diff --cc gdk/broadway/gdksurface-broadway.c
Simple merge

diff --cc gdk/gdkdisplay.c
Simple merge

diff --cc gdk/gdksurface.c
Simple merge

diff --cc gdk/wayland/gdkdisplay-wayland.c
Simple merge

diff --cc gdk/wayland/gdksurface-wayland.c
Simple merge

diff --cc gdk/x11/gdkdrag-x11.c
Simple merge

diff --cc gdk/x11/gdksurface-x11.c
Simple merge

diff --cc gtk/gtkshortcutcontroller.c
Simple merge

diff --cc gtk/gtkwidget.c
Simple merge

diff --cc gtk/gtkwindow.c
Simple merge