Add get_candidate_relations_to_delete (#92)

* Set a precise type for Model._meta

* Add missing 'get_candidate_relations_to_delete' function signature

Fixes https://github.com/mkurnikov/django-stubs/issues/77.

django-stubs/db/models/base.pyi

@@ -1,6 +1,7 @@
 from typing import Any, Dict, List, Optional, Set, Tuple, TypeVar, Union, ClassVar, Sequence, Generic
 
 from django.db.models.manager import Manager
+from django.db.models.options import Options
 
 class ModelBase(type): ...
 
@@ -10,7 +11,7 @@ class Model(metaclass=ModelBase):
     class DoesNotExist(Exception): ...
     class MultipleObjectsReturned(Exception): ...
     class Meta: ...
-    _meta: Any
+    _meta: Options
     _default_manager: Manager[Model]
     pk: Any = ...
     def __init__(self: _Self, *args, **kwargs) -> None: ...

django-stubs/db/models/deletion.pyi

@@ -1,6 +1,8 @@
-from typing import Any, Callable
+from typing import Any, Callable, Iterable
 
 from django.db import IntegrityError
+from django.db.models.fields import Field
+from django.db.models.options import Options
 
 def CASCADE(collector, field, sub_objs, using): ...
 def SET_NULL(collector, field, sub_objs, using): ...
@@ -9,6 +11,8 @@ def DO_NOTHING(collector, field, sub_objs, using): ...
 def PROTECT(collector, field, sub_objs, using): ...
 def SET(value: Any) -> Callable: ...
 
+def get_candidate_relations_to_delete(opts: Options) -> Iterable[Field]: ...
+
 class ProtectedError(IntegrityError): ...
 
 class Collector: