Avoid documenting private or external classes

There are a lot of monkey patches inside the code base but there's
no need to document external constants so let's remove them from
the documentation

Also, since there are monkey patches for some test cases classes,
there were sometimes both documented and sneaked under the wrong
section in the sidebar.

Finally, for future references, the `active_support/vendor`
folder has been originally ignored in https://git.io/vDqfA but
no longer exists.

[ci skip]

activesupport/lib/active_support/i18n_railtie.rb

@@ -2,6 +2,8 @@ require "active_support"
 require "active_support/file_update_checker"
 require "active_support/core_ext/array/wrap"
 
+# :enddoc:
+
 module I18n
   class Railtie < Rails::Railtie
     config.i18n = ActiveSupport::OrderedOptions.new

activesupport/lib/active_support/xml_mini/libxml.rb

@@ -74,5 +74,7 @@ module LibXML #:nodoc:
   end
 end
 
+# :enddoc:
+
 LibXML::XML::Document.include(LibXML::Conversions::Document)
 LibXML::XML::Node.include(LibXML::Conversions::Node)

railties/lib/rails/api/task.rb

@@ -8,8 +8,7 @@ module Rails
           include: %w(
             README.rdoc
             lib/active_support/**/*.rb
-          ),
-          exclude: "lib/active_support/vendor/*"
+          )
         },
 
         "activerecord" => {
@@ -69,7 +68,11 @@ module Rails
             README.rdoc
             lib/**/*.rb
           ),
-          exclude: "lib/rails/generators/rails/**/templates/**/*.rb"
+          exclude: %w(
+            lib/rails/generators/rails/**/templates/**/*.rb
+            lib/rails/test_unit/*
+            lib/rails/api/generator.rb
+          )
         }
       }
 

railties/lib/rails/test_help.rb

@@ -14,10 +14,12 @@ require "active_support/testing/autorun"
 if defined?(ActiveRecord::Base)
   ActiveRecord::Migration.maintain_test_schema!
 
-  class ActiveSupport::TestCase
-    include ActiveRecord::TestFixtures
-    self.fixture_path = "#{Rails.root}/test/fixtures/"
-    self.file_fixture_path = fixture_path + "files"
+  module ActiveSupport
+    class TestCase
+      include ActiveRecord::TestFixtures
+      self.fixture_path = "#{Rails.root}/test/fixtures/"
+      self.file_fixture_path = fixture_path + "files"
+    end
   end
 
   ActionDispatch::IntegrationTest.fixture_path = ActiveSupport::TestCase.fixture_path
@@ -27,6 +29,8 @@ if defined?(ActiveRecord::Base)
   end
 end
 
+# :enddoc:
+
 class ActionController::TestCase
   def before_setup # :nodoc:
     @routes = Rails.application.routes