Correct verifier merging of primitive arrays

Merging of primitive array types (e.g. float[][] + String[]) was being
handled by the general-purpose type merge, which was determining the
result to be an Object.  It should have been an Object[].

This changes the verifier to treat arrays of primitive as arrays, but
with one fewer dimension.

Bug: 3130586
Change-Id: I35a6c27256f69f142fa2a8c22bc5f995096c9ae1