[mlir] Add a TensorLoadToMemref canonicalization

A folder of `tensor_load + tensor_to_memref` exists but it only applies when
source and destination memref types are the same.

This revision adds a canonicalize `tensor_load + tensor_to_memref` to `memref_cast`
when type mismatches prevent folding to kick in.

Differential Revision: https://reviews.llvm.org/D97038