Set C# encoding to utf-8-bom

.editorconfig

@@ -13,6 +13,7 @@ trim_trailing_whitespace = true
 [*.{cs,csx,vb,vbx}]
 indent_size = 4
 insert_final_newline = true
+encoding = utf-8-bom
 
 # IDE0073: The file header is missing or not located at the top of the file
 dotnet_diagnostic.IDE0073.severity = error