This fixes the resolution of Rec10.Zero in ListSlices.td.
As part of this, correct the definition of complete for ListInit such that
it's complete iff all the elements in the list are complete rather than
always being complete regardless of the elements. This is the reason
Rec10.TwoFive from ListSlices.td previously resolved despite being
incomplete like Rec10.Zero was
Depends on D100247
One thing to mention about this function. Downstream, our test for this uses our !iscomplete() predicate but I'm not aware of a good way to test this upstream as the FieldInit::Fold change means it no longer controls whether FieldInit's successfully resolve.