Improve type hints of URL conf & include() (#949)

* Improve type hints of URL conf & include()

The type of `urlpatterns` list is `List[Union[URLPattern, URLResolver]]`.

* https://docs.djangoproject.com/en/dev/ref/urls/#django.urls.include
* https://docs.djangoproject.com/en/4.0/ref/urls/

* Alias _AnyURL = Union[URLPattern, URLResolver]

* Fix extract_views_from_urlpatterns

tests/typecheck/urls/test_conf.yml

@@ -1,9 +1,9 @@
 -   case: test_path_accepts_mix_of_pattern_and_resolver_output
     main: |
       from typing import List, Tuple, Union
-      from django.urls import path, URLPattern, URLResolver
+      from django.urls import path, _AnyURL
 
-      def include() -> Tuple[List[Union[URLPattern, URLResolver]], None, None]: ...
+      def include() -> Tuple[List[_AnyURL], None, None]: ...
 
       path('test/', include())
 
@@ -16,3 +16,31 @@
       def include() -> Tuple[List[URLPattern], None, None]: ...
 
       path('test/', include())
+
+-   case: test_urlconf_include
+    main: |
+      from typing import List
+
+      from django.conf.urls.i18n import urlpatterns as i18n_urlpatterns
+      from django.contrib.auth.views import LoginView
+      from django.contrib.staticfiles.urls import staticfiles_urlpatterns
+      from django.contrib import admin
+      from django.contrib.flatpages import urls as flatpages_urls
+      from django.urls import _AnyURL, re_path, include, path
+
+      foo_patterns: List[_AnyURL] = []
+
+      urlpatterns: List[_AnyURL] = [
+          path('login/', LoginView.as_view(), name='login'),
+          path('admin/', admin.site.urls),
+          re_path('^foo/', include(foo_patterns, namespace='foo')),
+          re_path('^foo/', include((foo_patterns, 'foo'), namespace='foo')),
+          re_path('^foo/', include(foo_patterns, 'foo')),
+          path('flat/', include(flatpages_urls)),
+          path('flat/', include((flatpages_urls, 'static'))),
+          path('i18n/', include(i18n_urlpatterns)),
+          path('i18n/', include((i18n_urlpatterns, 'i18n'))),
+          path('admindocs/', include('django.contrib.admindocs.urls')),
+          path('admindocs/', include(('django.contrib.admindocs.urls', 'i18n'))),
+          path('', include(staticfiles_urlpatterns(prefix='static/')))
+      ]