fix #14795: FP unusedStructMember when type is a template parameter #20294

Job	Run time
build_make (ubuntu:25.10)	3m 0s
build_cmake (ubuntu:24.04, true, true)	3m 2s
build_make (ubuntu:24.04)	17s
build_make (alpine:3.23)	5m 58s
build_cmake (ubuntu:25.10, true, true)	2m 45s
build_cmake (alpine:3.23, false, false)	4m 40s
build_make (ubuntu:24.04)	4m 45s
build_make (ubuntu:25.10)	3m 0s
build_cmake (alpine:3.23, false, false)	4m 40s
build_make (alpine:3.23)	5m 58s
build_cmake (ubuntu:25.10, true, true)	2m 45s
build_cmake (ubuntu:24.04, true, true)	3m 2s
	43m 52s

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