Generalized zero/sign-ext analysis. Generalized SAD.

Rationale:
The more, the better. Some of the analysis was
overly conservative (e.g. extension does not
need to happen from terminals only as long
as vectorized guarantees higher order bits
don't contribute). Also, added hidden-SUB for SAD.

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

Bug: 64091002
Change-Id: I66afd8fb4292ce5cf14f98f9c5ce2bf2b8c98488