Documentation fixes for the select_for_update change.

Refs #22343; thanks Tim Graham for the fixes.
Fixed #22412 -- More nuanced advice re template filters and exceptions.

Thanks Tim for review.
Fixed #22195 -- Used constants to define built-in tags for check framework.

Thanks Elvard for the patch.
Fixed #22194 -- Added --list-tags option to check command.

Thanks Elvard for the patch.
Refactored some code in SelectDateWidget.
Fixed #22364 -- Sanitized getpass input in changepassword.

Python 2 getpass on Windows does not accept unicode, even
when containing on ASCII characters. Related #190807.
Fixed #21353 -- Noted that description is ignored for TabularInlines.

Thanks nofinator for the report.
Fixed #22321 -- Wrapped exceptions in _set_autocommit.

Refs #21202.
Fixed #21239 -- Maintained atomicity when closing the connection.

Refs #15802 -- Reverted #7c657b24 as BaseDatabaseWrapper.close() now
has a proper "finally" clause that may need to preserve self.connection.
Fixed #21202 -- Maintained atomicity when the server disconnects.

Thanks intgr for the report.

This commit doesn't include a test because I don't know how to emulate a
database disconnection in a cross-database compatible way.

Also simplified a 'backends' test that was constrained by this problem.
Increased robustness of 58161e4e. Refs #22291.
Fixed #22419 -- Typo in docs/topics/db/multi-db.txt.

Thanks Josh Kupershmidt.
Improved a comment. Thanks intgr for the report.
Fixed #22102 -- Made SimpleTestCase tests run before unittest.TestCase ones

Thanks aptiko for the reporti and Tim Graham for the review.
Also allowed a non-overridden setting to be deleted

Refs #20032, #18824. Thanks ztorstri at gmail.com for the report.
Fixed #21760 -- prefetch_related used an inefficient query for reverse FK.

Regression introduced by commit 9777442. Refs #21410.
Fixed stray comment introduced by d3b71b9.

Thanks Claude Paroz for the report.
Fixed #22350 -- Consistently serialize bytes and text in migrations.

Thanks to @treyhunner and Loïc for their suggestions and review.
Fixed #22398 -- Added detail about callable in KEY_FUNCTION docs
Merge pull request #2541 from arachnegl/22398_KEY_FUNCTION_doc_detail

Fixed #22398 -- Added detail about callable in KEY_FUNCTION docs