Add private field naming rule to editorconfig (#1697)

.editorconfig

@@ -25,11 +25,24 @@ indent_size = 4
 
 [*.cs]
 indent_size = 4
+
 dotnet_diagnostic.IDE0005.severity = error
 dotnet_diagnostic.VSTHRD003.severity = none
 dotnet_diagnostic.VSTHRD103.severity = none
 dotnet_diagnostic.VSTHRD105.severity = none
+
+dotnet_naming_rule.private_members_with_underscore.symbols = private_fields
+dotnet_naming_rule.private_members_with_underscore.style = prefix_underscore
+dotnet_naming_rule.private_members_with_underscore.severity = suggestion
+
+dotnet_naming_symbols.private_fields.applicable_kinds = field
+dotnet_naming_symbols.private_fields.applicable_accessibilities = private
+
+dotnet_naming_style.prefix_underscore.capitalization = camel_case
+dotnet_naming_style.prefix_underscore.required_prefix = _
+
 dotnet_sort_system_directives_first = true
+
 csharp_style_namespace_declarations = file_scoped:warning
 csharp_prefer_braces = true:warning