Propagate for heap-allocated vars #15822

Job	Run time
regression (macos-latest, ocaml-variants.4.14.2+options,ocaml-option-flambda)	12m 8s
regression (ubuntu-latest, ocaml-variants.4.14.2+options,ocaml-option-flambda)	7m 44s
extraction	0s
	19m 52s

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