filterx: use ordered array for storing variables in FilterXScope #1404

Job	Run time
create-source-tarball	1m 44s
create-packages / debian-bookworm	6m 21s
create-packages / debian-testing	6m 25s
create-packages / fedora-39	6m 40s
create-packages / ubuntu-jammy	8m 17s
	29m 27s

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