Handle toJson properly on json resources (#30801)

At the moment when you call toJson on a Json resource it skips the `toArray` method and directly calls toJson on the Eloquent model because of the ForwardsCalls trait. This seems unwanted because if you're formatting the resource in a specific way through the toArray method you'd expect it to be honered when calling toJson I believe. toJson isn't documented on the Json Resources documentation but I still believe that this should be honered.

This is technically a breaking change so I'm targeting the next release.

Eloquent/JsonEncodingException.php

@@ -18,6 +18,20 @@ public static function forModel($model, $message)
         return new static('Error encoding model ['.get_class($model).'] with ID ['.$model->getKey().'] to JSON: '.$message);
     }
 
+    /**
+     * Create a new JSON encoding exception for the resource.
+     *
+     * @param  \Illuminate\Http\Resources\Json\JsonResource  $resource
+     * @param  string  $message
+     * @return static
+     */
+    public static function forResource($resource, $message)
+    {
+        $model = $resource->resource;
+
+        return new static('Error encoding resource ['.get_class($resource).'] with model ['.get_class($model).'] with ID ['.$model->getKey().'] to JSON: '.$message);
+    }
+
     /**
      * Create a new JSON encoding exception for an attribute.
      *