[VitisAI] support memory buffer contains the TensorProto external data (microsoft#22042)

### Description
Extend VitisAI EP `tensor_proto_as_raw` API to support memory buffer
containing the TensorProto external data


### Motivation and Context
For reduce peak memory usage, VitisAI EP need support ORT format model
and setting session option
`session.use_ort_model_bytes_for_initializers` for enable directly use
the model bytes for initializers.

Co-authored-by: mingyue <mingyue@xilinx.com>

Author: mingyueliuh

onnxruntime/core/providers/vitisai/imp/tensor_proto.cc

@@ -9,9 +9,44 @@
 #include "core/providers/shared_library/provider_api.h"
 namespace vaip {
 using namespace onnxruntime;
+
+static gsl::span<const char> process_ext_address(const ONNX_NAMESPACE::TensorProto& tensor) {
+  auto tensor_proto = const_cast<ONNX_NAMESPACE::TensorProto*>(&tensor);
+  auto file = std::string();
+  uintptr_t offset = 0;
+  size_t size = 0;
+  if (tensor_proto->data_location() == ONNX_NAMESPACE::TensorProto_DataLocation::TensorProto_DataLocation_EXTERNAL) {
+    auto external_data = tensor_proto->mutable_external_data();
+    auto external_data_size = external_data->size();
+    for (auto i = 0; i < external_data_size; ++i) {
+      auto& data = external_data->at(i);
+      char* end = nullptr;
+      if (*data.mutable_key() == "location") {
+        file = *data.mutable_value();
+      } else if (*data.mutable_key() == "offset") {
+        offset = (uintptr_t)std::strtoull(data.mutable_value()->data(), &end, 10);
+      } else if (*data.mutable_key() == "length") {
+        size = (size_t)std::strtoull(data.mutable_value()->data(), &end, 10);
+      } else if (*data.mutable_key() == "checksum") {
+        // checksum = (size_t)std::strtoull(data.mutable_value()->data(), &end, 10);
+      }
+    }
+    if (file == "*/_ORT_MEM_ADDR_/*") {
+      auto addr = reinterpret_cast<const char*>(offset);
+      return {addr, size};
+    }
+  }
+  return {};
+}
+
 gsl::span<const char> tensor_proto_as_raw(const onnxruntime::Graph& graph, const ONNX_NAMESPACE::TensorProto& tensor) {
   auto& mut_tensor = const_cast<ONNX_NAMESPACE::TensorProto&>(tensor);
   if (!tensor.has_raw_data()) {
+    auto maybe_external_memory_address = process_ext_address(tensor);
+    if (!maybe_external_memory_address.empty()) {
+      return maybe_external_memory_address;
+    }
+
     std::vector<uint8_t> unpacked_tensor;
     auto path = graph.ModelPath();
     auto s = onnxruntime::utils::UnpackInitializerData(tensor, path, unpacked_tensor);