Add tags.json and attributes.json files for Vetur

[posva]

See vuejs/vetur#2046

I think it makes sense to add a folder vetur and add the file paths to the package.json file like mentioned at https://vuejs.github.io/vetur/framework.html

cc @octref

[posva]

@octref let me know if I missed anything!

[octref]

It's already working (duplicates because Vetur bundles vue-router tags as well).

I'll send another PR that updates the tags/attributes.

[posva]

Ok, let me add them to current Vue Router as well and release a version in both so you can safely remove them from Vetur