Support owned iterators for GroupBy and IntoChunks `into_iter()` #948

Job	Run time
check format	5s
check	12s
check (--no-default-features)	23s
doc	7s
check (--no-default-features --features use_alloc)	16s
check (--all-targets --all-features)	19s
msrv	25s
semver-checks	2m 21s
test	51s
All checks succeeded	0s
	4m 59s

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