[executorch][serialization] Data serialization interface

Pull Request resolved: #7194

Introduce data serialization interface.
ghstack-source-id: 257299296
@exported-using-ghexport

Differential Revision: [D65947145](https://our.internmc.facebook.com/intern/diff/D65947145/)

Author: lucylq

exir/_serialize/data_serializer.py

@@ -0,0 +1,65 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import Dict, Sequence
+
+from executorch.exir._serialize._cord import Cord
+
+from executorch.exir.schema import Tensor
+
+
+@dataclass
+class SerializationInfo:
+    # A sequence of deduplicated tensor data.
+    tensor_buffers: Sequence[bytes]
+
+    # A map from tensor name (fqn) to tensor index inside `tensor_buffers`.
+    fqn_to_buffer_index: Dict[str, int]
+
+    # A map from tensor name (fqn) to tensor metadata. The `Tensor` type contains information related to how tensor data is stored (eg. `data_buffer_idx`, `allocation_info`, `extra_tensor_info`). These are not used; only the tensor metadata (eg. `scalar_type`, `dim_order`, `sizes`, etc.) are used.
+    fqn_to_metadata: Dict[str, Tensor]
+
+
+"""
+Abstract base class for custom serialization and deserialization of tensor data from ExecuTorch.
+Tensor data can be serialized into different formats. See executorch/extension/flat_tensor/ for an example.
+"""
+
+
+class DataSerializer(ABC):
+    @abstractmethod
+    def __init__(self) -> None:
+        """
+        This initializer may be overridden in derived classes to hold
+        the data required for serialization, eg. configurations.
+        """
+        pass
+
+    @abstractmethod
+    def serialize_tensors(
+        self,
+        serialization_info: SerializationInfo,
+    ) -> Cord:
+        """
+        Serializes a list of tensor metadata and tensors emitted by ExecuTorch
+        into a binary blob.
+
+        Args:
+            serialization_info: the tensor buffers and metadata required for serialization.
+
+        Returns:
+            A binary blob that contains the serialized data.
+        """
+        raise NotImplementedError("serialize_data")
+
+    @abstractmethod
+    def deserialize_tensors(self, blob: Cord) -> SerializationInfo:
+        """
+        Deserializes a blob into a list of tensor metadata and tensors. Reverses the effect of serialize_tensors, which serializes tensor metadata and tensors emitted by ExecuTorch into a binary blob.
+
+        Args:
+            blob: A binary blob that contains the serialized data.
+
+        Returns:
+            SerializationInfo: tensors and metadata that can be used to serialize data.
+        """
+        raise NotImplementedError("deserialize_data")