[ruby/json] Move create_addtions logic in Ruby.

By leveraging the `on_load` callback we can move all this logic
out of the parser. Which mean we no longer have to duplicate
that logic in both parser and that we'll later be able to extract
it entirely from the gem.

f411ddf1ce

test/json/json_addition_test.rb

@@ -151,7 +151,12 @@ class JSONAdditionTest < Test::Unit::TestCase
   end
 
   def test_deprecated_load_create_additions
-    assert_deprecated_warning(/use JSON\.unsafe_load/) do
+    pattern = /json_addition_test\.rb.*use JSON\.unsafe_load/
+    if RUBY_ENGINE == 'truffleruby'
+      pattern = /use JSON\.unsafe_load/
+    end
+
+    assert_deprecated_warning(pattern) do
       JSON.load(JSON.dump(Time.now))
     end
   end