Revert "Remove .future files for usedWithSync and usedWithSingle."

This reverts commit 2d6f5bf95a49b00d7d9b8a6248a7be25dc50403f.

Tom advised waiting to remove these futures until we'd had a group discussion on
the semantics of noinit for syncs and singles, so I'm reverting this change.
Rearrange the output to catch reversal cases.

If noinit were somehow using _defaultOf and the default case was skipping it
entirely, this test would not have caught that case.  Thanks, Tom, for pointing
it out!