Support 'tag' template helper within renderer

[Flauschbaellchen]

If using a custom renderer it is not possible to use the tag helper which is a shorter variant for content_tag and is preferred by Rails style guides.
The SimpleNavigation::Renderer::Base does not delegate tag to the template adapter.

Documentation:
rails/rails#25195
https://docs.rubocop.org/rubocop-rails/cops_rails.html#railscontenttag

It would be great to see this implemented.
Currently I've excluded any renderers from Rubocop's auto-correction feature.

[andi]

It would be great if you could contribute with a PR, thanks!