* menu: replace gtk_menu_popup() with gtk_menu_popup_at_rect()

Replace deprecated gtk_menu_popup() with gtk_menu_popup_at_rect(). This
provides the same menu positioning calculation while eliminating
deprecation warnings.

* ui: replace gtk_widget_get_realized() with gtk_widget_get_mapped()

Replace deprecated gtk_widget_get_realized() with
gtk_widget_get_mapped(). Since mapped widgets are guaranteed to be
realized, and we only care about widget visibility, this change
eliminates deprecation warnings while maintaining the same
functionality.

* frames: replace gdk_window_process_all_updates() with gdk_display_flush()

Replace deprecated gdk_window_process_all_updates() with
gdk_display_flush(). Both functions ensure pending updates are
processed, but gdk_display_flush is more general for all display
requests.

find . \( -name '*.h' -o -name '*.c' \) -exec sed -i 'N;/^\n$/D;P;D;' {} \;

This commit reverts:

https://github.com/mate-desktop/marco/commit/f0541e3dfda29c26fe14c9c9117f95c49006c75c
https://github.com/mate-desktop/marco/commit/d18c2fb4acb58c408c01700682b9922de86e8b2f

And it applies an alternative to fix the deprecated functions:

gdk_screen_get_width

gdk_screen_width
gdk_screen_height

partially taken from:
https://git.gnome.org/browse/metacity/commit/?id=542a2b4