[1.7.x] Fixed #22680 --  I/O operation on closed file.

This patch is two-fold; first it ensure that Django does close everything in
request.FILES at the end of the request and secondly the storage system should
no longer close any files during save, it's up to the caller to handle that --
or let Django close the files at the end of the request.

Backport of e2efc8965edf684aaf48621680ef54b84e116576 from master.
[1.7.x] Created a new tests folder (`model_options`).

And moved `tablespaces` option tests to it.
The new folder can be used to test models/options, like the new option
added in refs #22778.

Backport of 5a3ae7e260 from master
[1.7.x] Fixed #22653 -- Added some database feature flags to tests.

Thanks Rahul Priyadarshi.

Backport of 99f5ea9cc8 from master
[1.7.x] Fixed #22487: Separated schema migration from data migration in test

The data migration failed on Oracle, killing the entire test suite.

Thanks timo for reporting the Oracle breakage,
and andrewgodwin for suggesting the solution.

Backport of 64d94cf from master
[1.7.x] Added link to data migrations in initial data deprecation note

Backport of 4123f55c33 from master
[1.7.x] Fixed typo in docs/ref/forms/validation.txt.

Backport of c307383ec9 from master