[mlir][memref] Fix subview offset verification.

Offset-specific verification seems to have been lost in one of the recent refactorings.
Also add proper tests that would have caught this omission.

This addresses the immediate issues discussed in:
https://llvm.discourse.group/t/memref-subview-affine-map-and-symbols/4851

Differential Revision: https://reviews.llvm.org/D115427