allow PHP generator to accept modelNameMapping (#20533)

Author: Abraham-Flutterwave

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

@@ -501,6 +501,11 @@ private String toGenericName(String name) {
 
     @Override
     public String toModelName(String name) {
+
+        if (modelNameMapping.containsKey(name)) {
+            return modelNameMapping.get(name);
+        }
+        
         // memoization
         String origName = name;
         if (schemaKeyToModelNameCache.containsKey(origName)) {