fix #14795: FP unusedStructMember when type is a template parameter #20371

Job	Run time
build_cmake (ubuntu:25.10, true, true)	3m 26s
build_make (alpine:3.23)	6m 2s
build_make (ubuntu:24.04)	2m 38s
build_cmake (alpine:3.23, false, false)	4m 24s
build_make (ubuntu:25.10)	3m 50s
build_cmake (ubuntu:24.04, true, true)	5m 25s
	25m 45s

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