Summary:
These are not supported by any of the code using `type_cast`. In the general
case, such casting would require memrefs to handle a non-contiguous vector
representation or misaligned vectors (e.g., if the offset of the source memref
is not divisible by vector size, since offset in the target memref is expressed
in the number of elements).
Differential Revision: https://reviews.llvm.org/D76349
