Avoided split_exclude() for Q when used as an expression.

Refs #24503.

This was broken in c2bc1cef (refs #23763).

Thanks Wim Feijen for the report.

Thanks Markus Holtermann for review.

It has been superseded by the converter infrastructure.

Took advantage of the new database adapters and converters.

The primary use case is to interact with a third-party database (not
primarily managed by Django) that doesn't support time zones and where
datetimes are stored in local time when USE_TZ is True.

Configuring a PostgreSQL database with the TIME_ZONE option while USE_TZ
is False used to result in silent data corruption. Now this is an error.

This mirrors convert_xxxfield_value nicely, taking advantage of the
adapter/converter terminology which is commonly used by DB-API modules.

Refs #23820.

Fixed #19738.

Refs #17755. In order not to introduce a regression for raw queries,
parameters are passed through the connection.ops.value_to_db_* methods,
depending on their type.

Put the types in the same order and checked for None consistently.

Refs #23820.

Deprecation warning was introduced in https://bugs.python.org/issue24134

Thanks Carl Meyer and Tim Graham for the reviews.

Thanks Thomas Recouvreux for the report and Tim Graham for the tests and
review.

This fixes a regression with runtests.py --reverse after
bd53db5e

We need to avoid leaking model registration in the default AdminSite.

Thanks Luis Del Giudice for the report, and Aymeric Augustin and Markus
Holtermann for the reviews.