Improve pickling of HttpResponse instances

[zatro]

When pickling a HTTPResponse, rather than pickling all of its attributes just store what is needed for the creation of a new HttpResponse with the correct content, status code and headers.

See related discussion on ticket #23895 and its PR.

[Mariusz Felisiak]

Thanks, it's worth adding that pickling HttpResponse with CBV crashes:

>>> import pickle
>>> response = self.client.get('/cbv_view/')
>>> pickle.dumps(response)
...
AttributeError: Can't pickle ....

[tigicion]

​https://github.com/django/django/pull/14728

[Mariusz Felisiak]

I agree with ​Keryn's comment.

[Keryn Knight]

Tentatively setting the flag back; I've left feedback and proposed a first sketch of how adapting SimpleTemplateResponse and TemplateResponse might go.

[Anvesh Mishra]

Submitted the ​PR with all the suggested changes according to Keryn and Felix's comments on ​PR-14728

[Mariusz Felisiak <felisiak.mariusz@…>]

In d7f5bfd:

Fixed #32969 -- Fixed pickling HttpResponse and subclasses.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 173034b0:

Refs #34482 -- Reverted "Fixed #32969 -- Fixed pickling HttpResponse and subclasses."

This reverts commit d7f5bfd241666c0a76e90208da1e9ef81aec44db.

Thanks Márton Salomváry for the report.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 791407f:

[4.2.x] Refs #34482 -- Reverted "Fixed #32969 -- Fixed pickling HttpResponse and subclasses."

This reverts commit d7f5bfd241666c0a76e90208da1e9ef81aec44db.

Thanks Márton Salomváry for the report.

Backport of 173034b00589c083793d495e8b07e35be2cb1cf0 from main