gtk.cfg: Add pure annotations for more GLib functions (#8687) #20270

Job	Run time
build_make (alpine:3.23)	5m 55s
build_make (ubuntu:25.10)	5m 2s
build_cmake (alpine:3.23, false, false)	4m 38s
build_make (ubuntu:24.04)	4m 23s
build_cmake (ubuntu:24.04, true, true)	5m 31s
build_cmake (ubuntu:25.10, true, true)	5m 33s
	31m 2s

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