Check that non-phase ghosts are carried forward appropriately #15823

Job	Run time
regression (ubuntu-latest, ocaml-variants.4.14.2+options,ocaml-option-flambda)	7m 30s
regression (macos-latest, ocaml-variants.4.14.2+options,ocaml-option-flambda)	15m 1s
extraction	0s
	22m 31s

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