Add gdk_window_lookup, gdk_window_foreign_new, gdk_pixmap_lookup and

Add gdk_window_lookup, gdk_window_foreign_new, gdk_pixmap_lookup and

        * gdk/gdkwindow.h, gdk/gdkpixmap.h, gdk/x11/gdkx.h,
        gdk/x11/gdkwindow-x11.c, gdk/x11/gdkpixmap-x11.c,
        gdk/win32/gdkwin32.h, gdk/win32/gdkwindow-win32.c,
        gdk/win32/gdkpixmap-win32.c, gdk/linux-fb/gdkfb.h,
        gdk/linux-fb/gdkwindow-fb.c, gdk/linux-fb/gdkpixmap-fb.c:
        Add gdk_window_lookup, gdk_window_foreign_new, gdk_pixmap_lookup
        and gkd_pixmap_foreign_new to the gdk frontend api. (#62063)

        * gtk/gtkselection.c: Remove gdk backend dependencies. (#62063)