Ensure extract is seen as having scalar result.

Rationale:
Extracting from a vector yields a scalar, yet
our parallel mover and one DCHECK did not account
for that fact (note that moving towards a vector
type system will prevent such errors).

Regression test for this is part of the SAD CL.

Test: test-art-host test-art-target

Bug: 64091002
Change-Id: Id154edd1a069c54e7d8da069c368dea0a8f973f4