Fixed #30449 -- Fixed ordering of admin.RelatedFieldListFilter.

Refactored admin.RelatedFieldListFilter and admin.RelatedOnlyFieldListFilter
to respect ordering defined in related model admin. Refactored
Field.get_choices to fallback to default model ordering.

django/contrib/admin/filters.py

@@ -193,11 +193,19 @@ def has_output(self):
     def expected_parameters(self):
         return [self.lookup_kwarg, self.lookup_kwarg_isnull]
 
-    def field_choices(self, field, request, model_admin):
+    def get_field_ordering(self, field, request, model_admin):
+        """
+        Return the list of ordering fields for related field,
+        if related model admin has `ordering`.
+        """
         ordering = ()
         related_admin = model_admin.admin_site._registry.get(field.remote_field.model)
         if related_admin is not None:
             ordering = related_admin.get_ordering(request)
+        return ordering
+
+    def field_choices(self, field, request, model_admin):
+        ordering = self.get_field_ordering(field, request, model_admin)
         return field.get_choices(include_blank=False, ordering=ordering)
 
     def choices(self, changelist):
@@ -419,4 +427,5 @@ def choices(self, changelist):
 class RelatedOnlyFieldListFilter(RelatedFieldListFilter):
     def field_choices(self, field, request, model_admin):
         pk_qs = model_admin.get_queryset(request).distinct().values_list('%s__pk' % self.field_path, flat=True)
-        return field.get_choices(include_blank=False, limit_choices_to={'pk__in': pk_qs})
+        ordering = self.get_field_ordering(field, request, model_admin)
+        return field.get_choices(include_blank=False, limit_choices_to={'pk__in': pk_qs}, ordering=ordering)