Fix api_view decorator with Django 4

[tim-mccurrach]

Description

When using Django 4, we get slightly unexpected behaviour using the api_view decorator:

@api_view(["POST"])
def some_view(request):
    pass

# Django 3.2
>>> some_view.__name__
'some_view'
>>> some_view.__qualname__
'WrappedAPIView'

# Django 4.0
>>> some_view.__name__
'view'
>>> some_view.__qualname__
'View.as_view.<locals>.view'

Further Discussion

This change is caused by a change in the way that Django 4 implements View.as_view(). The change and a full discussion can be viewed here, but in short: as_view used to use update_wrapper and now it doesn't.

I was definitely for the change above, and argued against using update_wrapper in that case, but for a decorator such as api_view it is definitely appropriate, and I would expect things like __name__ and __qualname__ to be preserved from the original function.

When using a class-based view you have written, using view_class seems a reasonable approach. But in this case, the fact you have a class-based view is obscured unless you read the source code and so I think __name__ should be copied over.

[adamchainz]

Seems reasonable to me.