Add missing definitions to six.moves.http_client (#7615)

These were removed as a side-effect of #7327, which added
`__all__` to `http.client`. I checked that all the definitions
are present at runtime via `six.moves.http_client`.

stubs/six/six/moves/http_client.pyi

@@ -1 +1,61 @@
+# Many definitions are not included in http.client.__all__
 from http.client import *
+from http.client import (
+    ACCEPTED as ACCEPTED,
+    BAD_GATEWAY as BAD_GATEWAY,
+    BAD_REQUEST as BAD_REQUEST,
+    CONFLICT as CONFLICT,
+    CONTINUE as CONTINUE,
+    CREATED as CREATED,
+    EXPECTATION_FAILED as EXPECTATION_FAILED,
+    FAILED_DEPENDENCY as FAILED_DEPENDENCY,
+    FORBIDDEN as FORBIDDEN,
+    FOUND as FOUND,
+    GATEWAY_TIMEOUT as GATEWAY_TIMEOUT,
+    GONE as GONE,
+    HTTP_PORT as HTTP_PORT,
+    HTTP_VERSION_NOT_SUPPORTED as HTTP_VERSION_NOT_SUPPORTED,
+    HTTPS_PORT as HTTPS_PORT,
+    IM_USED as IM_USED,
+    INSUFFICIENT_STORAGE as INSUFFICIENT_STORAGE,
+    INTERNAL_SERVER_ERROR as INTERNAL_SERVER_ERROR,
+    LENGTH_REQUIRED as LENGTH_REQUIRED,
+    LOCKED as LOCKED,
+    METHOD_NOT_ALLOWED as METHOD_NOT_ALLOWED,
+    MOVED_PERMANENTLY as MOVED_PERMANENTLY,
+    MULTI_STATUS as MULTI_STATUS,
+    MULTIPLE_CHOICES as MULTIPLE_CHOICES,
+    NETWORK_AUTHENTICATION_REQUIRED as NETWORK_AUTHENTICATION_REQUIRED,
+    NO_CONTENT as NO_CONTENT,
+    NON_AUTHORITATIVE_INFORMATION as NON_AUTHORITATIVE_INFORMATION,
+    NOT_ACCEPTABLE as NOT_ACCEPTABLE,
+    NOT_EXTENDED as NOT_EXTENDED,
+    NOT_FOUND as NOT_FOUND,
+    NOT_IMPLEMENTED as NOT_IMPLEMENTED,
+    NOT_MODIFIED as NOT_MODIFIED,
+    OK as OK,
+    PARTIAL_CONTENT as PARTIAL_CONTENT,
+    PAYMENT_REQUIRED as PAYMENT_REQUIRED,
+    PRECONDITION_FAILED as PRECONDITION_FAILED,
+    PRECONDITION_REQUIRED as PRECONDITION_REQUIRED,
+    PROCESSING as PROCESSING,
+    PROXY_AUTHENTICATION_REQUIRED as PROXY_AUTHENTICATION_REQUIRED,
+    REQUEST_ENTITY_TOO_LARGE as REQUEST_ENTITY_TOO_LARGE,
+    REQUEST_HEADER_FIELDS_TOO_LARGE as REQUEST_HEADER_FIELDS_TOO_LARGE,
+    REQUEST_TIMEOUT as REQUEST_TIMEOUT,
+    REQUEST_URI_TOO_LONG as REQUEST_URI_TOO_LONG,
+    REQUESTED_RANGE_NOT_SATISFIABLE as REQUESTED_RANGE_NOT_SATISFIABLE,
+    RESET_CONTENT as RESET_CONTENT,
+    SEE_OTHER as SEE_OTHER,
+    SERVICE_UNAVAILABLE as SERVICE_UNAVAILABLE,
+    SWITCHING_PROTOCOLS as SWITCHING_PROTOCOLS,
+    TEMPORARY_REDIRECT as TEMPORARY_REDIRECT,
+    TOO_MANY_REQUESTS as TOO_MANY_REQUESTS,
+    UNAUTHORIZED as UNAUTHORIZED,
+    UNPROCESSABLE_ENTITY as UNPROCESSABLE_ENTITY,
+    UNSUPPORTED_MEDIA_TYPE as UNSUPPORTED_MEDIA_TYPE,
+    UPGRADE_REQUIRED as UPGRADE_REQUIRED,
+    USE_PROXY as USE_PROXY,
+    HTTPMessage as HTTPMessage,
+    parse_headers as parse_headers,
+)