Port hreflang tokens to D8

Just wanted to report that #33 fixed this issue for us.

Moving this to the v2 branch.

The patch from #33 also works for us.

Test coverage is missing, so leave it at needs work

The MR seems to be empty.

• Converted to MR and confirmed in tests that tags are displayed.
• Not sure how far you want to take token tests. I can't quite wrap my head around the TokenTestTrait at the moment.

scott_euser → changed the visibility of the branch 8.x-1.x to hidden.

scott_euser → changed the visibility of the branch 2.1.x to hidden.

scott_euser → changed the visibility of the branch 2956982-port-hreflang-tokens to hidden.

Further updated if you use `[node:url-LANGCODE]` you will get a fatal error otherwise because ->url() exists on translation but ->toUrl() is needed for entity interface

Patch #33 also works on the v2 branch

The issue fork is based on patch #27

Patch #33 and #27 have a different approach and the difference can be seen on comment #32

To sum up: with patch #33 the hreflang information can be filled in the "global" section of metatag and will be valid for the whole site, without having to fill in the information for the main sections of the various entities