[mlir][MemRef] Extend memref.subview sub-byte type emulation support. (#94045)

In some cases (see https://github.com/iree-org/iree/issues/16285),
`memref.subview` ops can't be folded into transfer ops and sub-byte type
emulation fails. This issue has been blocking a few things, including
the enablement of vector flattening transformations
(https://github.com/iree-org/iree/pull/16456

). This PR extends the
existing sub-byte type emulation support of `memref.subview` to handle
multi-dimensional subviews with dynamic offsets and addresses the issues
for some of the `memref.subview` cases that can't be folded.

Co-authored-by: Diego Caballero <diegocaballero@google.com>