Added SAD test. Generalized vector analysis of narrow type.

Rationale:
The new example shows that scalar type of array reference does not
reflect signed-ness or unsigned-ness of vector operation. Instead
the vectorizer's analysis looks at zero or sign extension to determine
what operation is required and passes this as explicit or implicit
attribute to the code generator. So don't use packed data type to
decide what operation to perform. This become relevant while switching
to explicit signed and unsigned data types, where we want to pass the
right type to make this decision in the future

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

Bug: 64091002

Change-Id: I49a8827a13dd703910effcb5a5ebc4b9646cd1e8