[mlir] Fix subview verifier.

The subview verifier in the rank-reduced case is plainly skipping verification
when the resulting type is a memref with empty affine map. This is generally incorrect.

Instead, form the actual expected rank-reduced MemRefType that takes into account the projections of 1's dimensions. Then, check the canonicalized expected rank-reduced type against the canonicalized candidate type.

Differential Revision: https://reviews.llvm.org/D95316