Rename `unroll_n_to_subgroups` to `subgroups_n` #31660

Job	Run time
setup / setup	8s
runtime_small	2m 3s
runtime_tracing :: tracy provider	1m 12s
runtime :: ubuntu-20.04	1m 14s
runtime_tracing :: console provider	52s
runtime :: windows-2022	2m 54s
runtime :: macos-14	1m 37s
summary	5s
	10m 5s

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