Add SQLite backend is_in_memory_db() functions (#1218)

* Add SQLite backend is_in_memory_db() functions

* Update django-stubs/db/backends/sqlite3/creation.pyi

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>

django-stubs/db/backends/sqlite3/base.pyi

@@ -26,6 +26,8 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     introspection_class: Type[DatabaseIntrospection]
     ops_class: Type[DatabaseOperations]
 
+    def is_in_memory_db(self) -> bool: ...
+
 FORMAT_QMARK_REGEX: Any
 
 class SQLiteCursorWrapper(Database.Cursor): ...

django-stubs/db/backends/sqlite3/creation.pyi

@@ -1,5 +1,11 @@
+from os import PathLike
+from typing import Union
+
 from django.db.backends.base.creation import BaseDatabaseCreation
 from django.db.backends.sqlite3.base import DatabaseWrapper
 
 class DatabaseCreation(BaseDatabaseCreation):
     connection: DatabaseWrapper
+
+    @staticmethod
+    def is_in_memory_db(database_name: Union[str, PathLike[str]]) -> bool: ...