Leverage JsonMarshal.GetRawUtf8Value for BinatyData construction (Azure#51172)

Author: live1206

sdk/resourcemanager/Azure.ResourceManager/src/Common/Custom/Models/ManagedServiceIdentity.Serialization.cs

@@ -263,7 +263,12 @@ internal static ManagedServiceIdentity DeserializeManagedServiceIdentity(JsonEle
                     Dictionary<ResourceIdentifier, UserAssignedIdentity> dictionary = new Dictionary<ResourceIdentifier, UserAssignedIdentity>();
                     foreach (var property0 in property.Value.EnumerateObject())
                     {
-                        dictionary.Add(new ResourceIdentifier(property0.Name), ModelReaderWriter.Read<UserAssignedIdentity>(new BinaryData(Encoding.UTF8.GetBytes(property0.Value.GetRawText())), options, AzureResourceManagerContext.Default));
+#if NET9_0_OR_GREATER
+                        var data = new BinaryData(JsonMarshal.GetRawUtf8Value(property0.Value).ToArray());
+#else
+                        var data = new BinaryData(Encoding.UTF8.GetBytes(property0.Value.GetRawText()));
+#endif
+                        dictionary.Add(new ResourceIdentifier(property0.Name), ModelReaderWriter.Read<UserAssignedIdentity>(data, options, AzureResourceManagerContext.Default));
                     }
                     userAssignedIdentities = dictionary;
                     continue;