gio: Add a method to get a stream of incoming connections to SocketListener #3748

Job	Run time
build GTK binaries with gvsbuild	14s
build gtk-rs on Windows (cairo, true, --features png,pdf,svg,ps,use_glib,v1_16,freetype,script,wi...	2m 34s
build gtk-rs on Windows (gdk-pixbuf, true, --features v2_42)	1m 43s
build gtk-rs on Windows (gio, true, --features v2_80)	3m 54s
build gtk-rs on Windows (glib, true, --features v2_80)	3m 51s
build gtk-rs on Windows (glib-build-tools, false)	1m 28s
build gtk-rs on Windows (graphene, false)	2m 27s
build gtk-rs on Windows (pango, true, --features v1_52)	1m 37s
build gtk-rs on Windows (pangocairo, true)	2m 48s
build gtk-rs on Windows (examples, false, --bins --examples --all-features)	1m 54s
	22m 30s

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