[3.9] bpo-46769: Improve documentation for `typing.TypeVar` (GH-31712) (GH-31941...

[3.9] bpo-46769: Improve documentation for `typing.TypeVar` (GH-31712) (GH-31941) (GH-32067)

* [3.9] [3.10] bpo-46769: Improve documentation for `typing.TypeVar` (GH-31712) (GH-31941)

* [3.10] bpo-46769: Improve documentation for `typing.TypeVar` (GH-31712)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
(cherry picked from commit 81b425d4dc43b60dd11a3e9abc5c84a4b8b384db)

* Remove references to `reveal_type`, add new section on `self` types.
(cherry picked from commit d5ed8a8258eaf7a241978b1b0aeb971108d0f7e0)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
* remove unused susp allowlist

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>