Moved _get_model_tuple() to the base Operation class.

This allows field and special operations to use this logic.

django/db/migrations/operations/base.py

@@ -1,4 +1,5 @@
 from django.db import router
+from django.db.models.fields.related import RECURSIVE_RELATIONSHIP_CONSTANT
 
 
 class Operation:
@@ -124,6 +125,14 @@ class Operation:
             return [self]
         return False
 
+    def _get_model_tuple(self, remote_model, app_label, model_name):
+        if remote_model == RECURSIVE_RELATIONSHIP_CONSTANT:
+            return app_label, model_name.lower()
+        elif '.' in remote_model:
+            return tuple(remote_model.lower().split('.'))
+        else:
+            return app_label, remote_model.lower()
+
     def __repr__(self):
         return "<%s %s%s>" % (
             self.__class__.__name__,

django/db/migrations/operations/models.py

@@ -1,7 +1,6 @@
 from django.db import models
 from django.db.migrations.operations.base import Operation
 from django.db.migrations.state import ModelState
-from django.db.models.fields.related import RECURSIVE_RELATIONSHIP_CONSTANT
 from django.db.models.options import normalize_together
 from django.utils.functional import cached_property
 
@@ -279,14 +278,6 @@ class RenameModel(ModelOperation):
             kwargs
         )
 
-    def _get_model_tuple(self, remote_model, app_label, model_name):
-        if remote_model == RECURSIVE_RELATIONSHIP_CONSTANT:
-            return app_label, model_name.lower()
-        elif '.' in remote_model:
-            return tuple(remote_model.lower().split('.'))
-        else:
-            return app_label, remote_model.lower()
-
     def state_forwards(self, app_label, state):
         # Add a new model.
         renamed_model = state.models[app_label, self.old_name_lower].clone()