make cycle, splitter, roundRobin, and until compatible with RefRange

[aG0aep6G]

Part of a series on issue 18657. Previously: #6346.
This concludes std.range and std.algorithm.searching. Everything else still needs to be checked.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✗	18657	normal	std.range and std.algorithm can't handle refRange

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "stable + phobos#6935"

[thewilsonator]

Apologies CircleCI is having problems and as its required I can't merge it, please ping me if I forget about this after it gets fixed.

[wilzbach]

CircleCi fix is here: #6936 (should be in master soon)

[WalterBright]

@aG0aep6G @thewilsonator @wilzbach @andralex There's something seriously wrong if this wacky code is needed in every save() function. I strongly suggest stopping these changes until RefRange is re-evaluated as to why it is in Phobos if it breaks straightforward algorithms.

[aG0aep6G]

There's something seriously wrong if this wacky code is needed in every save() function.

It doesn't have to be done with move. It can also be done with a constructor like you did in #6900 and #6903. The only thing that matters is that opAssign is avoided. I did with move, because that seemed the least intrusive to me (doesn't touch the interface at all).

Or if you guys decide that ranges shouldn't do opAssign, then we can just remove it from RefRange and that's it.