feat(php): add support for 'off' variable naming convention in AbstractPhpCodegen

Author: Mostafa Aghajani

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractPhpCodegen.java

@@ -451,6 +451,8 @@ public String toVarName(String name) {
             name = camelize(name, LOWERCASE_FIRST_LETTER);
         } else if ("PascalCase".equals(variableNamingConvention)) {
             name = camelize(name, UPPERCASE_FIRST_CHAR);
+        } else if ("off".equals(variableNamingConvention)) {
+            // return the name as it is
         } else { // default to snake case
             // return the name in underscore style
             // PhoneNumber => phone_number