Update on "[executorch][flat_tensor] DataMap implementation"

DataMap implementation that
* Loads a flat_tensor file
* Populates a map with {fqn: tensor} and {fqn: TensorLayout}.
* Makes tensor information available via the named_data_map.h interface.

For now, DataMap doesn't store the DataLoader.
- If/when tensors are in their own segments, DataMap should also store a DataLoader.

Differential Revision: [D67064580](https://our.internmc.facebook.com/intern/diff/D67064580/)

[ghstack-poisoned]

extension/flat_tensor/targets.bzl

@@ -8,8 +8,6 @@ def define_common_targets():
         ],
         exported_headers = ["flat_tensor_data_map.h"],
         deps = [
-            "//executorch/extension/flat_tensor/serialize:schema",
-            "//executorch/extension/flat_tensor/serialize:serialize",
             "//executorch/extension/flat_tensor/serialize:generated_headers",
             "//executorch/extension/flat_tensor/serialize:flat_tensor_header",
             "//executorch/runtime/core:core",