settings.h: forward declare `AddonInfo` (#8602) #19975

Job	Run time
build_cmake (ubuntu:24.04, true, true)	4m 50s
build_cmake (ubuntu:25.10, true, true)	4m 41s
build_make (ubuntu:25.10)	4m 51s
build_cmake (alpine:3.23, false, false)	3m 51s
build_make (ubuntu:24.04)	4m 29s
build_make (alpine:3.23)	6m 3s
	28m 45s

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