Update .editorconfig naming (#3927)

.editorconfig

@@ -76,3 +76,13 @@ csharp_using_directive_placement = outside_namespace
 
 # xUnit1004: Test methods should not be skipped
 dotnet_diagnostic.xUnit1004.severity = refactoring
+
+# Instance fields are camelCase and start with _
+dotnet_naming_rule.instance_fields_should_be_camel_case.severity = suggestion
+dotnet_naming_rule.instance_fields_should_be_camel_case.symbols = instance_fields
+dotnet_naming_rule.instance_fields_should_be_camel_case.style = instance_field_style
+
+dotnet_naming_symbols.instance_fields.applicable_kinds = field
+
+dotnet_naming_style.instance_field_style.capitalization = camel_case
+dotnet_naming_style.instance_field_style.required_prefix = _