Add accepted_renderer, accepted_media_type to Request and Response

[q0w]

I have made things!

ref: https://github.com/encode/django-rest-framework/blob/f113ab6b68e5ab8c395a93f168fe46c77c05b324/rest_framework/views.py#L434-L435
ref: https://github.com/encode/django-rest-framework/blob/f113ab6b68e5ab8c395a93f168fe46c77c05b324/rest_framework/request.py#L115-L118

Related issues

[intgr]

Thanks! Let's merge this and get a release out the door. We can improve this later.

[intgr]

I don't think these can actually be None? Looking at APIView.perform_content_negotiation(), it rather raises exception than returns None.

Same for parse_header_parameters(), it raises NotAcceptable if it can't find a match.

But still this PR is an improvement, I'll merge this and get a release out the door. We can improve this later.

[q0w]

but request may not have these attrs at all. There are hasattr checks after all

[intgr]

Yeah, there's no way to annotate 'possibly missing attribute' for classes. A code comment in pyi is best we can do.

But that's different from None. If the value may be missing but never None then I'd suggest to remove | None. Because that's even more misleading.