Rename `unroll_n_to_subgroups` to `subgroups_n` #31714

Job	Run time
setup / setup	6s
runtime_tracing :: tracy provider	1m 13s
runtime_tracing :: console provider	51s
runtime :: ubuntu-20.04	1m 31s
runtime_small	2m 9s
runtime :: windows-2022	3m 1s
runtime :: macos-14	1m 19s
summary	9s
	10m 19s

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