Fix unbound method call for JSONEncoder (#17970)

* Fix unbound method call for JSONEncoder

The way it is currently it will lead to unbound method error

```python
In [1]: import json

In [2]: json.JSONEncoder.default('object_here')
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-872fdacfda50> in <module>()
----> 1 json.JSONEncoder.default('object_here')

TypeError: unbound method default() must be called with JSONEncoder instance as first argument (got str instance instead)

```

But what is really wanted is to let the json module to raise the "is not serializable error" which demands a bounded instance of `JSONEncoder()`

```python
In [3]: json.JSONEncoder().default('object_here')
---------------------------------------------------------------------------
TypeError: 'object_here' is not JSON serializable

```

BTW: I think it would try to call `.to_json` of object before raising as it is a common pattern.

* Calling JSONEncoder bounded `default` method using super()

(cherry picked from commit b06fb2022c)

lib/ansible/plugins/filter/core.py

@@ -68,7 +68,7 @@ class AnsibleJSONEncoder(json.JSONEncoder):
         if isinstance(o, HostVars):
             return dict(o)
         else:
-            return json.JSONEncoder.default(o)
+            return super(AnsibleJSONEncoder, self).default(o)
 
 def to_yaml(a, *args, **kw):
     '''Make verbose, human readable yaml'''