Always use _typeshed.Self, where applicable (#6880)

* Always use `_typeshed.Self`, where applicable

* Revert changes to `google-cloud-ndb` (ambiguous)

* Remove empty line added by script

* Revert changes to `stubs/python-dateutil/dateutil/relativedelta.pyi`

* Manually add a few more that the script missed

* Improve `filelock` annotation

Source code here: https://github.com/tox-dev/py-filelock/blob/79ec7b2826e33b982fe83b057f359448b9d966ba/src/filelock/_api.py#L207

* Improve `opentracing/scope` annotation

Source code here: https://github.com/opentracing/opentracing-python/blob/3e1d357a348269ef54d67f761302fab93dbfc0f7/opentracing/scope.py#L71

* Improve `redis/client` stub

Source code here: https://github.com/redis/redis-py/blob/15f315a496c3267c8cbcc6d6d9c6005ea4d4a4d5/redis/client.py#L1217

* Improve `redis/lock` annotation

Source code here: https://github.com/redis/redis-py/blob/15f315a496c3267c8cbcc6d6d9c6005ea4d4a4d5/redis/lock.py#L155

* Improve `requests/models` annotation

Source code here: https://github.com/psf/requests/blob/d718e753834b84018014a23d663369ac27d1ab9c/requests/models.py#L653

stubs/requests/requests/models.pyi

@@ -1,4 +1,5 @@
 import datetime
+from _typeshed import Self
 from json import JSONDecoder
 from typing import Any, Callable, Iterator, Text, TypeVar
 
@@ -106,7 +107,7 @@ class Response:
     def __bool__(self) -> bool: ...
     def __nonzero__(self) -> bool: ...
     def __iter__(self) -> Iterator[bytes]: ...
-    def __enter__(self) -> Response: ...
+    def __enter__(self: Self) -> Self: ...
     def __exit__(self, *args: Any) -> None: ...
     @property
     def next(self) -> PreparedRequest | None: ...

stubs/requests/requests/sessions.pyi

@@ -1,4 +1,4 @@
-from _typeshed import SupportsItems
+from _typeshed import Self, SupportsItems
 from typing import IO, Any, Callable, Iterable, Mapping, MutableMapping, Optional, Text, TypeVar, Union
 
 from urllib3 import _collections
@@ -62,7 +62,6 @@ _Params = Union[
     Union[Text, bytes],
 ]
 _TextMapping = MutableMapping[Text, Text]
-_SessionT = TypeVar("_SessionT", bound=Session)
 
 class Session(SessionRedirectMixin):
     __attrs__: Any
@@ -80,7 +79,7 @@ class Session(SessionRedirectMixin):
     adapters: MutableMapping[Any, Any]
     redirect_cache: RecentlyUsedContainer[Any, Any]
     def __init__(self) -> None: ...
-    def __enter__(self: _SessionT) -> _SessionT: ...
+    def __enter__(self: Self) -> Self: ...
     def __exit__(self, *args) -> None: ...
     def prepare_request(self, request: Request) -> PreparedRequest: ...
     def request(