As per the docs [1]:
```
In absence of an explicit layout, a memref is considered to have a
multi-dimensional identity affine map layout.
```
This patch makes sure that MemRefs with no strides (i.e. no explicit
layout) are treated as contiguous when checking whether a particular
vector is a contiguous slice of the given MemRef.
[1] https://mlir.llvm.org/docs/Dialects/Builtin/#layout
Follow-up for #76428.
81df51fb31