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]

Author: lucylq

extension/flat_tensor/flat_tensor_data_map.h

@@ -57,7 +57,7 @@ class FlatTensorDataMap final : public executorch::runtime::NamedDataMap {
 
   FlatTensorDataMap(FlatTensorDataMap&&) noexcept = default;
 
-  ~FlatTensorDataMap() = default;
+  ~FlatTensorDataMap() override = default;
 
  private:
   FlatTensorDataMap(