Exploratory fix for non-deterministic processing of mixed contours and paths #2976

Job	Run time
fontc tests	1m 17s
resources/scripts/ots_test.sh	1m 7s
fontbe tests	58s
Rustfmt	1m 14s
Clippy lints	48s
tests other than fontbe,fontc	2m 19s
Build GS and check the result	3m 14s
cargo check no std	1m 38s
cargo test fea-rs	1m 7s
	13m 42s

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