community/gtk4.0: fix demo files being in main pkg
Move gtk4-demo, gtk4-widget-factory, gtk4-demo-application and their desktop files to the -demo subpackage, instead of just copying them. Also move gtk4-print-editor and gtk4-widget-factory demos.
CC: @Cogitri
Related: https://gitlab.com/postmarketOS/pmaports/-/issues/1029