fix typing on HttpResponse and StreamingHttpResponse (#712)

While the documentation for `HttpResponse` and `StreamingHttpResponse`
*says* `content` and `streaming_content` should be bytestrings [1] or an
iterable of bytestrings respectively [2], this is not what the API
supports [3] [4] and there are tests which make sure the API supports
more than bytestrings [5] [6] [etc]. Before assigning `content` or
`streaming_content` the code paths will call  `self.make_bytes` to
coerce the value to bytes.

[1]: ecf87ad513/django/http/response.py (L324-L327)
[2]: 0a28b42b15/django/http/response.py (L395-L399)
[3]: ecf87ad513/django/http/response.py (L342-L362)
[4]: 0a28b42b15/django/http/response.py (L415-L427)
[5]: 0a28b42b15/tests/cache/tests.py (L2250)
[6]: 0a28b42b15/tests/i18n/urls.py (L8)

tests/typecheck/views/test_function_based_views.yml

@@ -0,0 +1,102 @@
+-   case: http_response
+    main: |
+      from django.http.request import HttpRequest
+      from django.http.response import HttpResponse
+      from django.utils.translation import gettext_lazy as _
+
+      def empty_response(request: HttpRequest) -> HttpResponse:
+          return HttpResponse()
+
+      def str_response(request: HttpRequest) -> HttpResponse:
+          return HttpResponse('It works!')
+
+      def bytes_response(request: HttpRequest) -> HttpResponse:
+          return HttpResponse(b'It works!')
+
+      def object_response(request: HttpRequest) -> HttpResponse:
+          return HttpResponse(_('It works!'))
+
+-   case: http_response_content
+    main: |
+      from django.http.request import HttpRequest
+      from django.http.response import HttpResponse
+      from django.utils.translation import gettext_lazy as _
+
+      def empty_response(request: HttpRequest) -> HttpResponse:
+          response = HttpResponse()
+          reveal_type(response.content)  # N: Revealed type is "builtins.bytes*"
+          return response
+
+      def str_response(request: HttpRequest) -> HttpResponse:
+          response = HttpResponse()
+          response.content = 'It works!'
+          reveal_type(response.content)  # N: Revealed type is "builtins.bytes*"
+          return response
+
+      def bytes_response(request: HttpRequest) -> HttpResponse:
+          response = HttpResponse()
+          response.content = b'It works!'
+          reveal_type(response.content)  # N: Revealed type is "builtins.bytes*"
+          return response
+
+      def object_response(request: HttpRequest) -> HttpResponse:
+          response = HttpResponse()
+          response.content = _('It works!')
+          reveal_type(response.content)  # N: Revealed type is "builtins.bytes*"
+          return response
+
+-   case: streaming_http_response
+    main: |
+      from django.http.request import HttpRequest
+      from django.http.response import StreamingHttpResponse
+      from django.utils.translation import gettext_lazy as _
+
+      def empty_response(request: HttpRequest) -> StreamingHttpResponse:
+          return StreamingHttpResponse()
+
+      def str_response(request: HttpRequest) -> StreamingHttpResponse:
+          return StreamingHttpResponse(['It works!'])
+
+      def bytes_response(request: HttpRequest) -> StreamingHttpResponse:
+          return StreamingHttpResponse([b'It works!'])
+
+      def object_response(request: HttpRequest) -> StreamingHttpResponse:
+          return StreamingHttpResponse([_('It works!')])
+
+      def mixed_response(request: HttpRequest) -> StreamingHttpResponse:
+          return StreamingHttpResponse([_('Yes'), '/', _('No')])
+
+-   case: streaming_http_response_streaming_content
+    main: |
+      from django.http.request import HttpRequest
+      from django.http.response import StreamingHttpResponse
+      from django.utils.translation import gettext_lazy as _
+
+      def empty_response(request: HttpRequest) -> StreamingHttpResponse:
+          response = StreamingHttpResponse()
+          reveal_type(response.streaming_content)  # N: Revealed type is "typing.Iterator*[builtins.bytes]"
+          return response
+
+      def str_response(request: HttpRequest) -> StreamingHttpResponse:
+          response = StreamingHttpResponse()
+          response.streaming_content = ['It works!']
+          reveal_type(response.streaming_content)  # N: Revealed type is "typing.Iterator*[builtins.bytes]"
+          return response
+
+      def bytes_response(request: HttpRequest) -> StreamingHttpResponse:
+          response = StreamingHttpResponse()
+          response.streaming_content = [b'It works!']
+          reveal_type(response.streaming_content)  # N: Revealed type is "typing.Iterator*[builtins.bytes]"
+          return response
+
+      def object_response(request: HttpRequest) -> StreamingHttpResponse:
+          response = StreamingHttpResponse()
+          response.streaming_content = [_('It works!')]
+          reveal_type(response.streaming_content)  # N: Revealed type is "typing.Iterator*[builtins.bytes]"
+          return response
+
+      def mixed_response(request: HttpRequest) -> StreamingHttpResponse:
+          response = StreamingHttpResponse()
+          response.streaming_content = [_('Yes'), '/', _('No')]
+          reveal_type(response.streaming_content)  # N: Revealed type is "typing.Iterator*[builtins.bytes]"
+          return response