Output the URL of the entity in one main attribute

hrefLangcode is generally needed. If the the URL language detection is in place than hrefLangcode should be used as a prefix before path alias to make the path work.

implemented this and added a kernel test for the formatter. I think this formatter test-case is a good blue-print test-caes for further formatters, should be rather easy to copy and adapt it as needed.

> hrefLangcode is sometimes needed. If the the URL language detection is in place than hrefLangcode should be used as a prefix before path alias to make the path work.

actually, the output URL should just use the right language already. Then there is no need for the langcode anymore.

I made a setting to allow URLs to be absolute optionally though, that might be needed in some cases.

Note: This also adds service-utils as a new dependency. I think that's fine, we are going to tag 3.1 anyway. lupus_ce_renderer requires it already.

moving to rtbc

> I wonder whether we should test for other language.negotiation methods? I think the url.prefixes is the most widely used.

I do think that's not what we want to test here, generally they should be covered else. The test just makes sure that url-prefixes coming from it are correctley obeyed - if any.