Fix choices in ChoiceField to support IntEnum

Python support Enum in version 3.4, but changed __str__ to int.__str__ until version 3.11 to better support the replacement of existing constants use-case.
[https://docs.python.org/3/library/enum.html#enum.IntEnum](https://docs.python.org/3/library/enum.html#enum.IntEnum)

rest_frame work support Python 3.6+, this commit will support the Enum in choices of Field.

rest_framework/fields.py

@@ -8,6 +8,7 @@
 import uuid
 from collections import OrderedDict
 from collections.abc import Mapping
+from enum import Enum
 
 from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
@@ -1397,7 +1398,8 @@ def __init__(self, choices, **kwargs):
     def to_internal_value(self, data):
         if data == '' and self.allow_blank:
             return ''
-
+        if isinstance(data, Enum) and str(data) != str(data.value):
+            data = data.value
         try:
             return self.choice_strings_to_values[str(data)]
         except KeyError:
@@ -1406,6 +1408,8 @@ def to_internal_value(self, data):
     def to_representation(self, value):
         if value in ('', None):
             return value
+        if isinstance(value, Enum) and str(value) != str(value.value):
+            value = value.value
         return self.choice_strings_to_values.get(str(value), value)
 
     def iter_options(self):
@@ -1429,7 +1433,7 @@ def _set_choices(self, choices):
         # Allows us to deal with eg. integer choices while supporting either
         # integer or string input, but still get the correct datatype out.
         self.choice_strings_to_values = {
-            str(key): key for key in self.choices
+            str(key.value) if isinstance(key, Enum) and str(key) != str(key.value) else str(key): key for key in self.choices
         }
 
     choices = property(_get_choices, _set_choices)
@@ -1815,6 +1819,7 @@ class HiddenField(Field):
     constraint on a pair of fields, as we need some way to include the date in
     the validated data.
     """
+
     def __init__(self, **kwargs):
         assert 'default' in kwargs, 'default is a required argument.'
         kwargs['write_only'] = True
@@ -1844,6 +1849,7 @@ class ExampleSerializer(Serializer):
         def get_extra_info(self, obj):
             return ...  # Calculate some data to return.
     """
+
     def __init__(self, method_name=None, **kwargs):
         self.method_name = method_name
         kwargs['source'] = '*'