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.cpp

@@ -108,7 +108,8 @@ ET_NODISCARD Result<FreeableBuffer> FlatTensorDataMap::get_data(
 
   // This FreeableBuffer doesn't own the underlying data, and will not free it,
   // which is why the free function is a nullptr.
-  // TODO(T214294528)
+  // TODO(T214294528): Remove data_ro_ and instead load the data here, letting
+  // FreeableBuffer own it.
   return FreeableBuffer(
       static_cast<const uint8_t*>(data_ro_.data()) + metadata->offset(),
       tensor_layout_res.get().nbytes(),

extension/flat_tensor/flat_tensor_data_map.h

@@ -57,6 +57,8 @@ class FlatTensorDataMap final : public executorch::runtime::NamedDataMap {
 
   FlatTensorDataMap(FlatTensorDataMap&&) noexcept = default;
 
+  ~FlatTensorDataMap() = default;
+
  private:
   FlatTensorDataMap(
       executorch::runtime::FreeableBuffer&& flat_tensor_data,