Sort tensor list by name for serialization

- Tensors are stored in an unordered_map from mlir::Value::hash_value
  to tensor name.
- Before serialization, sort the tensor list alphabetically by name
  so that tensors always appear in a determinstic (and logical) order.

Signed-off-by: Jared Smolens <jared.smolens@arm.com>
Change-Id: I21c0e2ec04b7520e6a753b8bf62572a702002d5b